Stock Exhaust Performance Mod

Well I took the plunge and bored a hole in the end cap of the muffler inside the pipe (not the pipe end cap / spark arrester). If you remove the pipe end cap/spark arrester and look into the stock pipe about 8-10 inches you will see that the pipe does not have an opening for the exhaust to flow straight through it. Instead there is a solid metal cap right in the center of the pipe and the exhaust has to back up and find its way through a small hole in the side of the barrel. This is tremendously restrictive. I'm not a fan of loud bikes, so I was apprehensive for quite a while. I had recently found a stock pipe on ebay, so I bought it in case my experiment did not work out. I started out with drilling a 3/4 inch hole right through the center of the muffler cap inside the pipe (again this is not the spark arrester end cap of the pipe). I had to purchase a long metal drill bit for this job. The largest size I could find was a 1/2 bit that was about 12 inches long. Drilling through the cap was pretty easy, but you have to watch it when it breaks through as the drill can torque out of your hands and get pulled in toward the pipe. You can feel when it is about to go through, so just back off the pressure and be ready to stop the drill. You aren't going to hurt anything deep in the pipe once the drill goes through, just watch that drill doesn't torque into the pipe hurting your hands. After I got the 1/2 drill through I changed over to a tapered drill grinding wheel that goes from a point to about 3/4 inch. These are made out of grinding wheel stone type of material and are designed to fit in a drill chuck. I had to purchase a drill bit extension to put the grinding wheel in so I could use it inside the pipe. I was able to grind out the hole to 3/4 inch. I then decided to get rid of the diverter fins on the spark arrester. These are the little fins at the end of the spark arrester that are there to spin the exhaust. I ground the welds off with a grinder, then took a pair of pliers and worked the metal back and forth until they broke off. Then I smoothed everything that was left down with the grinder.
I then started the bike with the spark arrester off to blow out any debris that was left in there from the drilling and grinding. I then put the spark arrester / pipe end cap back on and it was time to test it out.

On starting the bike I heard no real increase in noise level. If there is one it is slight. Went for a ride and thought I detected a bit better performance, but it was hard to tell. So I removed the spark arrester and went for a ride. Definitely noisy without the spark arrester in, but there was also better performance. Nothing earth shattering, but definitely gained 1-2 hp. So I went back and decided to open up the pipe some more. The idea was to make the hole in the muffler cap about as big as the inside diameter of the header pipe. I used some more different types of drill grinding wheels to make the hole bigger. I was able to open it up to about 1 + 1/8 inch diameter, which is the inner diameter size of the stock header pipe. I went out for a test ride without the spark arrester in. Wow its loud now, but it also gained some extra power too. I bet without the spark arrester in place, and with the 1 + 1/8 inch hole in the muffler end cap, this is close in performance to aftermarket exhausts costing $400. Those exhausts usually claim an extra 3-4 hp, and I figure I gained about 2-3hp. Well riding it this way is obnoxious, so I decided to put the spark arrester back in and test it that way, fully expecting to loose the hp gains I made, and for the sound to still be too loud. Surprise! I lost almost no performance with the spark arrester back in, and it is almost as quiet as it was stock. Yeah!! So all in all I am very happy with the results. I did check the spark plug and it seems like it is maybe a hair lean, but still chocolate brown. I plan on rejetting the carb anyhow with a 42.5 pilot, 130 main, and raise the needle up a bit, so I may see even a bit more performance after that is done. The bike definitely pulls harder with this setup, as I just rode the bike stock over the same area right before I made the mods, and could definitely feel the difference. 2-3 hp is not earth shattering, but it was cheap to do. Something just bothered me about that muffler being so capped off. I have seen restrictive mufflers before, but this was one of the worst I have ever seen.
[img]http://www.geocities.com/z-1.geo/Index.html?1137808855404[/img]

Tried to upload a few pictures of this mod, but no luck. Maybe someone can write a step by step on how to get pictures uploaded on here? Anyhow I posted the pictures here for now.

http://www.geocities.com/z-1.geo/Index.html?1137808855404

[ February 13, 2006: Message edited by: Splatman ]

Thanks Slatman. It would be nice to know how to post pictures here.

Hi Z1XT225,

That was a great posting.

You've planted a seed in my to do list.

I'd like to hear more after you do the jetting. BTW what year is your XT225?

Brs,

Don V.

Glad to help "Z1XT225".. (Even though you left a " p " out of my name)
" Click " for instructions " How To Add Pictures To Your Posts ".. Cheers

Sorry Splatman about omitting the P before. For some reason the pictures you posted are no longer here?

Don

I have a 2002 XT225. And I will report back after rejetting the carb. Still waiting on my new main jet to arrive.

I think the Image Crown web site is down right now, that is why the pictures aren't showing up Splatman.

Z1XT225:

I have sent you a Private message.

Thanks for posting the results of your experiments.

Hi Z1XT225,
Did you get a chance to look down into the new hole you cut or try to push a wire through it to see if there were any other restrictions on the way down to the head pipe.What I was curious about is was there a single "baffle" or a series of them.
Paco

Hi paco

From what I can see through the hole these is nothing on the other side of the muffler cap. Looks like all the muffling is done through the muffler cap and spark arrester. After expanding the hole to 1 + 1/2 inch in diameter, and then running it without the spark arrester in, it sure seems to confirm this too, as it sounds like a straight pipe with megaphone. Very loud without the spark arrester in, but very reasonable with it installed.

I opened up the hole in the muffler end cap to 1 + 1/2 inch with great results! A guy named Jay in the Yahoo XT225 group mentioned that the hole in my original picture did not look to be an inch or more wide, which it indeed turned out not to be that big. The item I was using to measure the hole was not acurate so I have since started using a different method of measuring the hole and have it pretty accurate now. At any rate I opened the hole up to 1 + 1/2 inch diameter. I was able get some additional power out of the engine by doing this. With the spark arrester out it is real loud, kind of fun, but way loud. The bike really pulls great with the exhaust opened up like this, but is too loud. With the spark arrester back in the sound is a bit louder than with the smaller hole, but totally reasonable. When idling or minimal throttle you don't notice a lot of difference from stock. There is a bit more noise than stock at full throttle acceleration, but it is still very acceptable. I am very happy with the results of this mod. More power and a minimal increase in exhaust noise. I will probably take the spark arrester out every so often just to have some obnoxious fun, but for 99% of the time the spark arrester will stay in.

BTW: The reason I did not go ahead and open up the exhaust to the barrel size of 2 inches is that I thought it might make the barrel less stable. With that 1/4 rim still left around the muffler barrel end cap it keeps things nice and tight in there.

Paco's question got me to thinking that it would be interesting if someone replaced the muffler assembly inside the pipe with a silencer and packing instead. Since there looks to be nothing other than the muffler and spark arrester in the pipe, you could remove the muffler totally and insert the right size silencer with packing in the muffler area. At the end of the pipe (not the spark arrester or muffler) around the rim of the end of the pipe there is a weld that is holding the whole muffler assembly in place from what I can see. Theoretically you could grind that weld off and remove the whole muffler from the pipe. Then if you could find the right size of round silencer, you could insert it in place of the muffler and you would have a straight through pipe with a built-in silencer. You could secure it with stainless steel sheet metal screws through the outside of the pipe and you would have it. I'm not going to do it, as I am more than happy with the results of my experiment, but it would be a pretty slick mod.

Hey Z1,

Man, you've been really pushing the envelope on a stock exhaust! I've experimented quite a bit with a variety of reversible stock exhaust mods and carefully tracked the mileage with each one.

The profile of the stock exhaust flairs out like a megaphone and then there is that spherical shape to reflect the exhaust pulses back to the engine. I believe the length and shape of the exhaust is tuned to produce a very flat torque band especially in the lower to mid rpm range, which is where most riding is done.

I suspect what gains you are getting in the higher rpm range by better exhaust flow, equal a loss in low rpm torque due to the loss of the tuned reflected exhaust pulse. Low end torque also requires a certain amount of backpressure.
Which is why the stock hole in the sphere is 3/4 inch... the same as the exit hole in the stock spark arrestor.



This is a home made exhaust mod insert I built from copper plumbing fittings, which yields an average mileage gain of just under 4 mpg due to increased low end torque (a function of mileage). It is free flowing, and VERY mellow sounding.

You might consider making something similar as it would quiet down the bike considerably, and yet retain a smooth straight flow through design which does not compromise low end torque. Now maybe low end torque is not an issue for you, and flat out top end performance is more important, if it is...

...open it up, and put in big jets!

I know you are enjoying experimenting, because I also enjoy tinkering with this amazingly versatile little bike.

Take Care,


Greg

[ January 24, 2006: Message edited by: Greg ]

Hi Greg

I do not notice any loss of low end torque doing this mod. If fact the opposite is true; there is better pulling power than before all through the range. I too was apprehensive about modifying the exhaust thinking that there would be a trade off somewhere along the power range, but in fact the mod has increased the power throughout the entire range. I too figured Yamaha had done their homework to figure out exactly the right amount of back pressure needed when designing the exhaust the way they did, but that turns out not to be the case. I think Yamaha was more focused on creating a fool proof spark arrester that would pass all the government regulations rather than being focused on creating an exhaust that metered out the correct flat torque curve with a minimal amount of noise. The bottom line from my experiments is that the stock exhaust is way too restrictive for this engine. It is so restrictive that it basically nullifies any tuning effect of back pressure on the power curve. The restriction and back pressure is so great with the stock pipe that it does not come close to the threshold of where you can tune the exhaust with too little or too much back pressure. Plain and simple it is plugged up so bad in its stock form that it would be like running a marathon and trying to exhale out of only one nostril of your nose, with your other nostril plugged up and your mouth closed. Even with the 1 + ½ hole I ended up drilling in the exhaust, which is almost like running an open pipe without the spark arrester in it; the power curve is only enhanced with no ill effects to the low end power. The way I can really tell about the low end power increase is when I go up long incline hill and I am able to pull one higher gear than I usually would, even with the new 16 tooth countershaft sproket I installed. I can also tell by riding on flat ground and choosing two gears higher than what I would normally do, allowing the engine to lug down low and then opening up the throttle. With the stock pipe I would feel very little increase in power if I lug it down that low and then open the throttle up. I would normally need to gear down to get an increase in power in that situation. With the exhaust opened up I can open up the throttle and get more pulling power without having to go down a gear. I do suspect there is even more power gains to be had by increasing the intake flow through the airbox and rejetting the carb to run richer. Yamaha probably figured the intake airbox volume specifications taking into account the limited exhaust flow, and the ability for the engine to only require that limited intake of air, so there are probably gains to be made there for sure. I will report back as my progress toward XT225 Nirvana continues.

Hey Z1,

Ok... you are the one who knows, as I haven't actually tried what you've done.

I'm just going by my own experience in that when I did the exhaust mods, I couldn't trust my own subjective perception that more noise felt like more power. Which is why I did impartial mileage tests on everything I tried and compared them to the bone stock mileage, because they gave impersonal objective answers as to what worked the best.

However... I might just try what you did...

The only thing holding me back is a persistent aversion to doing irreversible mods on expensive parts.

Thanks for sharing your experience and describing it so completely, I'm really enjoying reading your words.

Take Care,


Greg

Hi Greg

Keep in mind I am not really focused or concerned about keeping the MPG up on my bike. So if that is your aim I would not go down this road. My focus is in allowing the motor to develop all the power it can throughout the range while keeping the exhaust pretty quiet. I would expect that by the time I am done with rejetting the carb and opening up the airbox to increase the flow there, I will indeed lose some MPG in the process. More power usually does equate to more fuel used. Allow more fuel and air to enter the combustion chamber, and you get more power.

Hi Folks,
I ended up boring a 7/8th inch hole in the back of the pipe. I chose that size as it matched the size of the opening in my custom endcap. With the endcap out the sound is very racy but crazy loud for anything other than pissing off the neighbors.It has that "burble" on downshift that sounds amazing. However as I value whats left of my hearing and try not to be the neighborhood pariah ,I put the 7/8th inch cap back on. I have a 130 main jet. a 1/16th inch spacer on the needle. a 40 pilot at 3 turns out.Stock airbox and snorkel with the screen removed. I found you do get a noticeable increase in upper rpm power and no noticeable loss on the bottom. Perhaps even a small increase but thats pretty subjective.I plan on temporarily removing the snorkel and see if it makes a difference. Just my nickels worth Z1XT225 you will notice an improvement with a larger main jet. I ride mostly at sea level to about 2000 feet and going from a 125 to a 130 was a big boost.
All I can say about the exhaust mods is that is one constipated stock pie that can easily be improved with a new endcap and about 20 min wrk with a drill and a cone shaped grinding bit!!!

It must be close to lunch time .I said pie instead of pipe. So much for "project literacy"

Hi paco

Great to hear someone else finding the joy of giving the stock pipe a decongestant fix. If you think a 7/8ths hole sounds cool, you should hear how deep the exhaust note is with a 1 + 1/2 hole in it, with no spark arrester in place. Incredibly loud, but very sexy as well. You really get the megaphone effect with a hole that big in the muffler.

I plan on rejetting the carb this week. I live right at sea level and plan on raising the needle valve a bit, installing a 42.5 pilot jet and a 130 main jet. I am also going to experiment with removing the side panel of the air box to see if I can tell any significant difference in allowing the airbox to suck in more air.

i did what you did too, Paco. 7/8 hole, but my end cap is 3/4. close enough for me. i never tried actually riding it without the spark arrester or my own end cap. way way too loud. i still can't wheelie the bike though with a 14/45 gear arrangment. i use a Unifilter and i shimmed the needle the normal amount. didn't mess with the jets though. i'm at 1000 feet.

Jay,

If you haven't, definately take the carb top off and open up the vacuum passage. This makes a big difference in throttle response.

Z1XT225,

Let me know where you got your 42.5 pilot for the Mikuni. I just got one from Motorcycle superstore and it is the nonbleeder type 151.067 - the correct type but looking at it it seems to have just a slightly different contour. Length is the same.

Hi Jay,
I would check your spark plug and see how it looks. Mine looked like new after 2500 km with the 125 main jet. I prefer a little richer and cooler jetting , which also improves your power at 3/4 throttle and up. I too have a 14 tooth front sprocket and its a great all round gearing choice, but you will lift the front wheel better with a larger rear sprocket.
I havent hogged out the vacuum port in the carb yet. I suspect you will get a more abrupt throttle response both rolling on the throttle and off. This may help loft the wheel but with a cv type carb one of its stock charicteristics is a smooth application of power.
If you do it let me know what you think.
Paco

i had the carb top off when i shimmed the needle, but i chose not to ream out the hole. i kept thinking, "why didn't yamaha do it to begin with."
i might try that some other time.

you can order the 42.5 pilot jet from your yamaha dealer. the part # is 4G0-14142-42-A0
torsten

stu35


Torsten has the correct part number, but the 42.5 pilot jet does look slightly different from the 40 stock pilot. The 42.5 has threads almost to the end of the large portion of the jet, where the stock 40 jet has its threads start a bit further down the jet. I really don't think you need the 42.5 pilot jet anyhow if you have the Mikuni carb. I tried it along with raising the needle and ended up going back to the stock 40 pilot and stck needle position because it was too rich down low, and wanted to stumble sometimes. I did change the main jet to a 130 and that seems to be working ok.

Z1XT225,

You are exactly right about the pilot's appearance. I put it in last night and it is correct - fitment that is. This is my wifes bike and she doesn't want me to up the power like I do on my bike. But it is nagging me about the less than ideal starting and slow warm up time. Hopefully this will help.

A little trick I did for times when the bike has sat a long, long time - I added a clear piece of tygon tubing plugged into a hole in the air box, ran it under the seat along the frame and exiting between the seat and side panel (never see it unless you look close). Prior to starting just give the tube end a squirt of starting fluid and it fires right up. No need to get a screwdriver and take off a side panel.

In about 1.5 months I will let you know how the 42.5 pilot helps. Reaming the vacuum on the carb top was a great improvement - Jay go for it.

Stu

Hey Z1,

I had exactly the same experience when I tried a 42.5 pilot, and also ended up going back to the 40. I think the *California* carb has a different taper profile to the needle, different main, and air jets which match the 40 pilot, and changing it without changing all of the other interconnected metering systems just messes things up.

Greg

Hi Greg

My bike is from Texas (no CA canister), but I would agree that the newer Mikuni carbs do not need the 42.5 pilot jet or the needle raised. I am at sea level and have done the exhaust mods and even tried it with the airbox wide open without the cover on, and the bike still ran too rich right off of idle to 3/4 throttle. A person might be able to get away with running the 42.5 pilot if you lower the needle slightly. This would probably produce better starting, and about the same level of performance as the 40 pilot with stock needle position.

Hi Stu35

The 42.5 pilot will most certainly improve starting the bike cold. I assume you have already removed the plug on the bottom of the carb to give you access to adjusting the pilot screw. That helps for sure. From the sound of your message you must have a pre 2002 model of XT225? The reason I say that is that you mention that you reemed out the plastic vacuum airway in the carb top on your bike. My 2002 XT225 did not need this mod at all, as it was already the correct size. The UK mod of reeming this airway out called for an 11/64 drill, but I found that on my carb that size was inacurate. The hole size on my carb is actually 5/32, which matches the hole/port on the metal part of the carb that it mates to. Seems like the UK mod is definately aimed at pre 2002 Mikuni stock carbs. I don't know when the change was made, but I know my 2002 did not require the UK carb mods except for opening up the pilot screw.

Z1XT225,

Yes my wifes is a 2001 US model (non-cali) and the carb vacuum definately did have a smaller port on the top compared to the carb body. I ran the bike friday night with the 42.5 pilot. Started good and can't comment on the warm up since it is still 30 degrees here. Once warm, there was only a slight hesitation when snapping the throttle from closed to wide open. There was none before (the vacuum ream really helped this last year before the ream I could not get rid of it). This I think I can eliminate with an adjustment on the fuel screw. Currently, I think it is 2.75 turns out. I love putzing!

Hi Z1XT225,
You will find out as I did that opening up the airbox in some fashion will give a good increase in power at 3/4 throttle and up. I started a new post under the "Alternative to airbox mod" heading. Its a lot easier to modify the airbox side cover.

Hey Z1!

I want to thank you for your really great idea of opening up the stock pipe. Now that I did it, I'm totally pleased!

After completely removing the barrier with a 1 13/16 hole saw, I made a funnel shaped insert specifically designed to pick up the exhaust right where the hole was. Well... It didn't work very good. The 3/4 inch tube was 7 inches long, and it was just too restrictive. So next, I'm going to try a 7 inch long 1 inch tube.

However... on a whim, I put the stock spark arrestor back on just to see how it would run.

Man, the bike came to life!

Now I have to start all over with a mileage test, as I've been changing things faster than I've been logging the miles to test them. But I can already tell... this mod really WORKS!!!

YOU DA MAN!!!!!!!

Greg

[ February 19, 2006: Message edited by: Greg ]

Z1 and Greg, I'd like to do this myself, but I have some questions for you:
Greg: did you use a normal hole saw (one sold for use on wood), or was it a special one designed for metal? also, why did you use 1 13/16", vs. the 1 1/2" that Z1 used?
Z1: why did you grind the fins off? did this help improve performance? finally, this is probably a dumb question, but I won't know if I don't ask... why does opening it up like this make such a big difference when ultimately the path of the exhaust ends with the stock 3/4" spark arrestor opening?

Thanks for your help! This is on my short list to do...

Hey James,

It's a metal hole saw, and consists of an arbor with a 1/4 inch twist drill in the center, and a round saw toothed cup attached. The metal is pretty soft and thin, so I think you could probably get away with a wood holesaw if you didn't have anything else. If you use a wood saw, keep the cutting speed slow so that it doesn't get hot. It doesn't take long to cut through.



I used 1 13/16 because it was the largest hole saw that fit and turned freely inside the pipe. I figured if I was going to make a hole, I might as well just take the whole damn thing out.

Just remember that it's an irreversible mod, and it makes using the copper cap exhaust mod really loud. However... the stock spark arrestor works suprisingly well! I'll let you know how the mileage test for this mod turns out. I'm really curious to find out, as the bike runs so good!

Take Care,


Greg

[ February 19, 2006: Message edited by: Greg ]

Greg:

Thanks for your kind words, and I am pleased to hear about someone else finding the same joy that I did in this mod. This experiment was just looming there for me; you know... should I or shouldn't I do it? I just wasn't happy knowing how plugged up that stock exhaust was. Well when I acquired another stock exhaust off of ebay I was free to go for it and am so glad I did. The stock spark arrester works great in the modified pipe, especially with the fins removed.

The next mod that increases the performance of the engine, almost as much as this exhaust mod does, is opening up the airbox. Paco did it the quick and easy way with some holes in the side cover, but I am going to go after the airbox itself. I got a new airbox for about $9.00 from the Yamaha dealer, so I am going to do this mod when I get the time. The whole trick for me is to create more flow in the airbox without increasing the noise factor. It isn’t that hard to do, but I need to find the right items to make it a clean and quiet setup. If you want to see the difference it can make take the side cover completely off of the airbox, but put the plastic cosmetic side cover back on the bike to keep from possibly loosing the filter. Only do this experiment on the street where it is clean, and not in dusty or dirty conditions. Now take a few spins up and down the street. You will see how the torque of the bike comes alive with the airbox opened up. It has a nice snap to it right off of the bottom and through the gears.


James:

Removing the fins off of the spark arrester just helps the exhaust flow a bit better around the inner arrester pipe. If you look at the fins you will see that they are almost the diameter of the 2-inch hole in the exhaust. That means that most of the exhaust is forced to go through the small openings in diverter fins; which isn't all that big if you look at them from the stand point of very little exhaust can escape around the outside of them.

As for your other question: "why does opening it up like this make such a big difference when ultimately the path of the exhaust ends with the stock 3/4" spark arrestor opening?"

Well the big problem with the stock exhaust is not that the opening in the end of the pipe is so small (3/4 inch), but the route that the exhaust has to take in order to get out of the pipe is nothing short of a complete maze of stops, and back tracks in order for it to get out of the pipe. These dead end obstructions create a sort of reverse pulse inside the pipe. If you take off the spark arrester and look into the pipe with a flashlight you will see that about 8-10 inches inside the pipe there is a dead end steel obstruction (muffler end cap) in the middle of the pipe. Now look carefully and you will see a 3/4-inch hole in the side wall of that inner muffler. That is the only way the exhaust can escape through the muffler. Now keep in mind that the exit hole is on the side of the inner muffler wall. The inner muffler wall is about 2-inches in diameter and the outer pipe wall is about 3 + 1/2 inches in diameter, which means that there is an open space between the inner muffler wall and the outer pipe wall. Since the normal flow of the exhaust is cut off by the inner muffler end cap right in the center of the pipe, the exhaust is first diverted into that open space between the inner muffler wall and the outer pipe, and not out the hole in the side of the muffler. It then it bounces back and is met by the on-coming exhaust pulses from the engine. These exhaust gases and pulses pressurize inside the pipe, and the exhaust is forced out of the side of the inner muffler wall. Next the exhaust gases squeeze through the spark arrester diverter fins, and then run dead end into the end of the spark arrester cap. Again a reverse pulse is generated by hitting the end cap and pressure is created that then forces the gases out through the arrester wire mess and ultimately out through the end of the pipe. All this restriction creates a tremendous amount of back pressure in the pipe, which in turn makes it difficult for the piston to push the exhaust out of the engine. This is why the stock exhaust is such a poor performer. Now without getting too complex here, the engine puts out exhaust pulses at a certain rate, of course depending upon the RPM's that the engine is turning. If most of the initial exhaust pulse is allowed to easily exit the engine and enter the pipe without having to overcome much pressure; it is a good thing for sure. In fact what pipe manufacturers usually try to accomplish is to time the way the exhaust pipe handles the exhaust pulses from the engine so that you actually create a vacuum in the pipe at just the right timing. If you do it right the exhaust is actually pulled out of the exhaust port instead of it having to be pushed out by the piston. So much for the basic idea. By opening the stock pipe up to the natural flow of the exhaust pulses from the engine; and by eliminating the major dead ends to the path of the exhaust, we create less reverse pluses and thus less back pressure in the pipe itself. So even though there is still only a 3/4 inch opening in the end of the pipe, we have greatly increased the ability of the pipe’s volume to handle the exhaust pulses coming from the engine. Without the reverse pulses the pipe flows much better. I hope all that was clear enough for you to get the idea behind it. In two words, it works.

Well I could not leave well enough alone; I gutted the rest of the inner muffler and baffles in my stock pipe. I would not recommend anyone else attempt this feat for two reasons. It is very difficult to do without cutting up and wrecking the pipe, and there is no real performance gains by doing it. I even tried running the pipe completely open without the spark arrester in it. Incredibly loud, but no performance gain. In fact I'd say I lost some power. What I did find out by doing this is that I finally reached the point of where there was too little back pressure. You need a bertain amount of back pressure in the pipe for optimal performance. The bone stock pipe is too restrictive and plugged up, while the completely gutted open pipe doesn't offer enough back pressure. Doing the original mode of drilling a hole of 1 + 1/2 - 1 + 7/8ths directly in the inner muffler end cap seems to be as good as it gets. When this mod is used with the stock spark arrester (with or without fins) seems to yield the right amount of back pressure for this engine. This is why I can't see that an aftermarket "performance" exhaust is going to yield much, if any more performance over the stock modified pipe that I did in this thread. I see no need to go out and spend $300 - $400 on an after market exhaust unless you just want a lighter weight exhaust system.

Hey Z1,

Do you mean that you actually took all of the interior can out? Wow... how were you able to do that? It looks impossible to do. I'm still shooting for a budget of under a hundred bucks to cobble together a modified Cobra pipe, but have no idea how well what I'm going to do will work.

You might try reinserting a short section of metal car exhaust tubing, or thinwall electrical conduit (EMT) to surround the stock spark arrestor and restore some backpressure.

Take Care,


Greg

Hi Greg

Yes it was a crazy project, and one that I would never recommended anyone else attempt. It took a combination of Sawzall with a long blade, Dremel, Hammer, Punch and Chisel. It was a long arduous process that I tried to abort several times before actually completing it.

The gutted pipe actually works fine in terms of back pressure with the spark arrester installed, but there are no performance gains, and the gutted pipe with no spark arrester is actually a performance loss. The original modification of drilling an inch and a half hole + in the inner muffler end cap works great and is about as good as it gets for this bike. I always have my other stock exhaust to fall back on. I will probably just drill a hole in the inner muffler end cap on that exhaust and call it a day.

Through this process I did find out the limits of how much back pressure is needed for optimal performance. It also showed me that I am really not missing much in terms of a performance gain from not using an aftermarket exhaust system. An after market exhaust might have a slightly more efficient internal design, but there is not a lot to be gained in terms increasing the flow of exhaust. The stock XT225 engine just can't handle much more flow other than that which can be gained by drilling a hole in the inner muffler end cap hole of the stock exhaust.

Hey Z1,

I know that that's like... you just gotta find out for yourself. It's really good you have another exhaust as a backup.

Took a ride today, and my bike has never run so good as with your stock exhaust mod. Thanks for taking the risk and sharing the results.

Take Care,


Greg

A note on comparing the bone stock exhaust to the "hole in the inner muffler end cap" modified stock exhaust. I installed my other by bone stock exhaust this weekend and ran the bike that way for two days. What I noticed is that the bone stock exhaust makes the bike run hotter; at least the exhaust header pipe itself gets hotter in comparison to the modified exhaust with a hole in the inner muffler end cap.

Guess I'll try a variant of this theme also, particularly since Greg so liked-it (and, because the young-man I purchased my XT from punched holes in bottom-plate with a screwdriver, already!). Once I weld other 'driver-holes' in the outer 'doughnut' that holds the tube-assy in there (!), I'll start with a modest 1 or 1-1/4" hole, and use with a de-finned SA (once I locate one...the lad REALLY liked 'loud'!) .
Would all agree, then, that this mod "adds very little to noise-level" with stock SA in? And Greg, have you checked mileage-impact on yours yet, and would that be with your 'HomeDepot-cap' (with or without larger opening?) or the SA in-place during mileage-check?
Also, and when combined with a Uni and slight snorkle-mod, would the consensus be that the resultant 'leaning' may call for a 2-mm Spacer/130 Main/42.5 Pilot for sea-level riding?

[ March 08, 2006: Message edited by: MeAlsoToo ]

Hi Me,

I would have like to run the 3/4 hole cap, but it was just too loud, so instead I ran the 1 inch funnel insert and it got an average of 90.3 mpg. I believe the stock Spark Arrestor would get something similar to that as it also ran very well. But I'm sidetracked now with the Cobra exhaust.


Gotta tell you... so far the Cobra has yielded only slightly more mileage improvement over the stock opened exhaust which is a super good mod...

...but I'm still in the beginning stages of tweaking it.

Take Care,


Greg

MeAlsoToo


I found on my 2002 XT225 that rejetting was really unneccessary after the exhaust mod, and even with the airbox wide open. The 42.5 pilot caused a slight stumble, so I went back to the stock 40 pilot. I had also raised the needle, but found that was also not needed. I also had installed a 130 main jet, which I still have installed, but even that increase was not needed, but it also did not really hurt performance. Removing the pilot plug and adjusting the screw out to about three full turns is all that was needed at sea level. I think jetting will depend on what year your XT is. Some of the older XT's seem to need more jetting changes than the newer ones.

All I can say is that I just did a 1 1/4 drill with a hole saw on my 06 and the bike runs great. It is the only thing that I did so far but adds a big improvement from the stock configuration. Praises to Z1XT225 for taking the risk for me and everyones input to build my confidence enough to attempt this modification. I can't wait to ride it into work tomorrow!

Scrape

Great to hear about your exhaust mod pleasure.

I recently drilled an 1+7/8ths hole in my other stock exhaust with an 1+7/8ths metal hole saw. The hole saw works really well for this mod. You can fish the metal plug out of the pipe with an extension magnet. Works great.

I've been comtemplating this mod. My only concern is how much louder the bike will be. What does it sound like with the spark arrestor still in place and bored out (probably 1 1/4")?

hey mf,

It's louder in a more deep and throaty way with the stock spark arrestor... but not obnoxiously so. I really like the sound. The bike has decidedly more low end torque. I'm sure of this because I'm running a 16T countershaft sprocket and am now easily able to run in sixth gear at much lower speeds than before. This has measurably improved the mileage. You don't need to do any mods to the arrestor. Just leave it as it is. Mine ran super with no changes.


Greg

I was lucky that the plug stayed on the drill bit and I didn't have to fish it out. We thought alike with the extension magnet though because I got out the metal cuttings with it but had to tape the edges of it up first because it kept sticking to the sides of the pipe on the way in. I probably should have just gone into the attic and gotten the shop vac but it was there in the tool box already and I used it.

Yes mf01, just as Greg said...throaty... and it burbles when you downshift. It also has kind of a growl to it...I love it! I read that Paco thought he would be the neighborhood pariah but I think that it is just fine for most neighborhoods. I get up early and my wife and kids did not wake up or complain but then again the windows were closed and the summer may lend new concerns. I don't see the stock configuration as being much different, that early in the morning. I am very happy with the modification for both performance and sound. I do have to admit that I ripped the screen off the spark arrestor...it is as efficient at collecting carbon as it does sparks. I have some stainless screen that I can wire on if the woods get dry in the summer months.

[ March 10, 2006: Message edited by: Scrape ]

[ March 10, 2006: Message edited by: Scrape ]

Oh yeah...the Cobra exhaust looks great on the bike too Greg.

Hi Scrape,
The sound of the modified pipe is very pleasing UNLESS you run it without the end cap. I havent attracted any undue attention when running a cap of some form. Now on occasion I have run my briggs n stratton lawn mower with a homemade open header but thats another story.
Paco

Hey paco,
you shouldn't have wrote about a mod on an exhaust of a lawnmower, Greg will want to do a cheap'n'nasty thing to his !

Jon

mf01

What is so cool about this mod is that it doesn't make the exhaust all that much louder than stock, but it makes it sound better as others have attested to. It is a bit louder than stock under full throttle acceleration, but you can also just back off the throttle a bit and it is almost as quiet as the stock exhaust is. When I am crusing around in places I want to keep the noise down, like leaving my neighborhood, I just back off the throttle a bit and it is a non-issue. I actually like that I am able to adjust how quiet or noisy the bike gets.

After having run the modified exhaust for several weeks, I tried my other bone stock exhaust and I discovered a couple of things. The bone stock exhaust makes the engine run hotter, and I also noticed that I did not like the super quiet exhaust in traffic. There is an advantage to being able to be louder when you want to, and in traffic it is a good thing because drivers are much more aware that a motorcycle is next to them if they can hear it.

One more tip is if you are going to do this mod go for the full 1+7/8ths metal hole saw. It's perfect for this mod and makes the inner hole that you drill with the saw line up directly with the 2" exit hole in the pipe. By the time the 1+7/8ths hole saw wallos a bit in cutting the hole, it ends up right at 2".

Nice to see some good info for the Serow.

I've just swapped over from a '96 XR200 on which I'd modified the airbox, exhaust & jets to a '92 Serow which needs pretty much the same treatment.

I'm not seeing an easy way to mod the exhaust on the serow though. It looks to be all welded into place, no screws that I can see.
Has anyone done a mod on one of these?

Hey Eh,
Look underneath the end cap and you will find a hole about 1/2 inch in diameter. Just inside that hole is the machine screw that you remove to pull the end cap out. If you have an older xt be advised that rust and fouling have likely welded the end cap in place. They can be a bitch to remove in this case.

I took the plunge and cut out the entire baffle inside the pipe and sure enough it did flow a bit better than the 7/8 inch hole I had in before. Not too loud but nice and deep sounding. Worthwhile unless you are looking for ulra low noise. I dont know why anyone would need to run in "stealth mode" unless you are running it where you shouldnt be.

Paco

I'm not seein' it...

http://goonan.no-ip.info/motorcycles/XT225/Exhaust/index.htm

The reason you dont see it is because it is a different exhaust than we have here in the states I have never seen this one and am not sure what advice to give you. Ours all Have a longer pipe hanging out the back of it with a hole and a screw in it to get to the spark arrestor yours doesnt even look to have a spark arrestor or else you would be able to get at it to clean it.

Hi,

I have a similar exhaust to EH-Holden, it is on the 90's Serow's and is completely sealed with no removable parts unless you create them with a hacksaw!. In my pursuit of a stainless steel exhaust silencer I have bought second hand from ebay a 2005 stock Yamaha WR250F silencer, once I had uprated my mig welder with stainless wire & argon gas I will get creating. All results will be posted, I have high hopes as I do with all my serow mods. For owners with the 90's style exhaust I believe you can modify them with a TTR250 derived mod, check the following link:-

http://www.ttr250.com/#Can%20I%20modify%20the%20exhaust%20to%20improve%20power?

See diagrams of standard & modified in section b)

Regards

Robin

Thanks for the replies.
It might be easier for me to adapt something else rather than hack around with the original one. I'll keep you posted as to what I end up doing.

hi to all.

Id like to perform this exhaust mod on my xt225,
but i just need some info.(I have no idea how exhaust system are made and how they work....)

The spark arrestor that all are talking about, how do i remove it? Do i have to open the whole exhaust system or can i just remove it by drilling and working from the outside end of the pipe?
Please anyone help, many thanx...

Alnico57

It will depend on what year XT225 you have. The removable spark arrester that we are talking about is connected to the exhaust end cap. The end cap / spark arrester is held in the pipe by a single screw under the end cap. If you look under the end cap you will see a hole that is where the set screw is. This screw can be very difficult to remove. It is best to take the pipe off and soak the screw in WD-40 for a while before trying to remove it. Then use a hammer activated impact driver to remove the screw, or you will round off the head and have to drill it out. You can see a picture of the end cap / spark arrester on page #1 of this thread. Splatman was kind enough to post the pictures. If your exhaust looks like this one

http://goonan.no-ip.info/motorcycles/XT225/Exhaust/index.htm

then it is does not have a removable end cap / spark arrester.

Many thanx, ill let u know if that goes alright!

Hey alnico57 !
just notice where you're from, wich area in Quebec are you from ? There is also Richard from montreal on this forum. Great people here. What kind of riding do you do (dirt-street-both) ? I mostly use mine on the streets but I ride in the dirt about every 2 weeks. I still have to wait about 2 weeks to get it out for the season, a lot of snow here in Quebec city.

Jon

Jon

Im from Quebec city, Uptown, and i got my xt225 last year on October.
I only had one month of fun and it was time to put the bike aside coz around here u have a white shitty thing call Snow...
Anyway now im getting the bike on the street next week and this week is Upgrade week.
Intake, exhaust, Carb...
Can't wait to see this exhaust mod on mine....
I got the bike for getting to the airport quickly(Very quickly...)
Anyway....hi to all the riders in Quebec!!

Thanks Z1:
I´m new in the group. I did the "hole" yesterday, and the beast woke up!!! Even with the spark arrester on, sounds like an XR 600....
Luckily, in Chile we have very poor noise legislation, even it´s rare that a policeman would ask for your papers!!! . So I´m enjoying the sound. I agree that the gain is substantial, around 3-4 hp, wich is a lot for such a small engine...
Thanks again, this weekend I´m hiting the dunes, so I will tell you how it performs off-road!!!

Hi Sergio,

Z1's stock exhaust mod deserves the award for the BEST XT MOD!

There is no other stock mod that makes as much difference in performance as that one.


Greg

I agree with Greg. This is the best single change. Add all the other lower impact mods and you end up with something pretty dramatic over stock.

I would like to do this mod, however although I cant get the end of the silencer off. I got the screw out after some troubles, but the end is rusted in. Does anyone have any great ideas on what could break it free?

Maybe a jujubee? Just don't tell Jay :p

But seriously, try squirting WD-40 all around the circumference, gently tap it with a hammer through a wood block to break up the rust, then try a strap wrench to twist it loose.

I take my spark arrester out regularly to clean the mesh. I put anti seize compound on the lip to protect it from the problem you describe.

Brs,

Don V.

Hi Yammyman:
Had the same problem, high temperatures do this with metal...
Anyway, I did the W-40 , then with a rubber hammer hit gently the sides of spark arrester. This will not take it off, but will loosen it.
Then, insert a thick metallic part (like a screwdriver) in the outer hole of the spark arrester...You DID remove the screw, did you?.
And finally, hit hard over the screwdriver shaft with a metallic hammer, the spark arrester will come off easily..
Good luck.
Sergio

Oooops : When I said "outer hole of the spark arrester" I meant the hole on the side, made for the screw.... . Put the screwdriver on the hole (perpendicular), hit the shaft of it, of course facing backwards... This should do it..
Sorry, but I´m not a native speaker...(although my spanish leaves much to be desired...).
Saludos Amigo...Enjoy the new sound of "the hole".

1.5 inch hole saw and an air drill at the local mechanic's shop. Rode 30 miles and have to agree with everyone else about the + nature of this mod across the powerban. But, I seriously think the bike is considerably louder, even with the arrestor. I like it that way though.
For the comments on the carb mods given here, am I to belief that with an 06 model the only part of the carb I need to tweak is the fuel mixture screw? I have some spacers I could try.

Canada Snow Man , I lived in Colorado Springs for 13 years. Keep your 4x4 loaded with weight and snow tires for winter.

Down here in SoCal we have a very change of ride. If you want snow go to mountains. If you want very dry cold ride in the Desert in winter. I really wanted to do the Death Valley ride... arrrggggggggg

So I took a look at removing the spark arrestor and it's going to have to be drilled out. How have you guys gone about drilling it out? Do you drill the top off of the screw to get it out? Once it is out how will it stay back on?

One thing you should remember as you work on the pipe. This I learned from trial and error and listening to Mike. If you make the air escape faster and the air intake faster you may need to get the carb / fuel/ air / adjusted depending on your elevation. In some cases some do not. There are some other ads you can make that may let you not have to change any jets. I should have gone to a 130 main jet recomended by FMF but went to a 127.5 and am going to carry a modified side airbox pannel for high elevation. All I can say is try and buy.... you will know when you have the hummer... mine is now very nice...

Sergio

Great to hear you are enjoying the success of this mod.


mf01

I assume you are talking about drilling out the screw that holds the end cap in place. You don't want to use a drill big enough to damage the threads. In fact what you really want to do is go to Sears and get one of their new extractor drill bits in the correct size. It is a fairly new item they sell, and it is designed to grab a hold of the messed up screw head. You use it with your drill in reverse mode, or counter clockwise mode. It is designed to drill in and grab the screw, and then extract it all at the same time with one bit. It works really well. The old way was to buy an EasyOut extractor. You would drill a hole right through the center of the screw, using a smaller bit than the screw size, and then use the EasyOut to screw into the hole counter clockwise to extract the screw.

i might have mentioned this earlier, i dont remember. i couldn't get my screw out either so i banged on it using a hammer and a ....crap, i can't remember the name of it. you smack the end with a hammer and the phillips head tip drives into the screw and turns ever so slightly counter clockwise. oh, what are they called???

anyway, i later found out that the force of hammering on the screw kinda buggered the threads, so i had to retap them to quarter inch. everything was fine, after that.
and for people living in the usa, i have heard that PB Blaster is the best product for unseizing stuck metal parts. and now i can't remember what you call solvents that unstick things. my mind is now useless. i do, however,remember that i am hungry for JuJuBees.

[ April 23, 2006: Message edited by: jay ]

I got it out without drilling it. I ended up spraying it WD40 and let it sit overnight. Then I took my dremel like tool and created a flat head slot out of the striped out screw. I think the grinding on it actually helped free it a little. Finally I took my impact wrench with a flat bit and it came out. I went to home depot and replaced it with a hex head bolt. I didn't get around to drilling the hole in the canister yet, but I picked up a 12" extension and 1 1/2" bi-metal hole saw.

Z1...I did your exhaust mod to Deb and My 06' XT's. It went very smooth. Removing the fins on the SP was easy as well by taking a pair of channel loc's and bending them back and forth untill they broke off, then grinding down the leftover knub with a bench grinder. Deb is still learning to ride and was having trouble killing the motor when taking off, but the power gained from your exhaust mod has helped. It seams to have enough bottom end grunt to pull her out without killing the motor. And I love the power all through the rpm range, and of course the sound is cool too.
Thanks Z1 !!!!!

Your Welcome!

Last week my 2001 XT225 was completely stock. I bought it used a couple of months ago with 2200 miles on the odometer. I had ridden it a couple of hundred miles, but I was getting bored with the bike, it just didn't have any snap.

I was thinking about selling it, but I decided to see what I could do to improve it. I'm handy with the tools, and the list of mods mentioned on this site seemed easy enough, not to mention vitually free of cost.

So, over the last few days I've done the full UK carb mod, pulled the airbox snorkel, and cut out the exhaust baffle plate with a 1-7/8" hole saw.

I also adjusted the valves, changed the motor oil to Mobil 1 15W-50, cleaned the stock air filter, and installed a new standard NGK sparkplug.

The carb mod made the bike start much better, and run a lot smoother too. But that exhaust mod really put some bark in it! In stock form it just felt and sounded kind of "piffy". But it runs and sounds like a REAL motorcycle now!

It's quite a bit louder than I expected, perhaps I should have started with a smaller hole in the baffle, after all you can always make them bigger. But that raspy sound when you roll off the throttle sounds nasty-good. And man, does it go!

I'll probably get a UNI filter, and I may get a larger main jet, too. But these basic mods cost nothing, and it's amazing how much more tractable power the bike makes after doing them.

Thanks for all the good info you guys post here, it sure makes it easy to own and tweak this little motorcycle.

Ed.

I bought a 2006 XT225 last Friday. I've been browsing this site for info and it looked like this mod was the first to perform. I just finished it today with 122 miles on my bike. Whew! Everything everone is saying is true. I can pop a wheelie in first and second gear easily. Wooooo Hoooooooo!!!

Thank You Z1XT225!!
Von

Your Welcome Von. Enjoy your new bike.

I used this site to break in my motor. And Yahooo !! your are right....

http://www.mototuneusa.com/break_in_secrets.htm

Searaider

Here in NZ we call 'em "impact drivers" but, considering that a lot of tools have different names in The US, the UK and NZ, that may not be useful to you - consider "crescent" vs "adjustable wrench".

Hi Wolf,

We call them impact drivers here too, and they're a really handy low tech tool. It's such a beautifully simple and practical principle that the instant the bit is driven into the head the tightest, it turns.

My 1965 Yamaha had all phillips head case bolts, and the only thing that could remove them without destroying them was an impact driver.

Take Care,

Greg

It's about the only thing that'll properly remove bolts with munted heads, too.

Philips head bolts are a pain in the arse, especially on engines because the bolts corrode into place and when you try to remove the bolts with a philips tip screwdriver you wind up stripping out the slots because the metal is usually crap.

One of my friends worked on my GSX250 and replaced the philips head bolts he removed with hex head bolts - the ones that require "Allen keys" ("Hex keys"), not a socket or spanner. Much more robust than the philips heads.

The problem with normal hex headed bolts that require a socket, is that there's always the risk that someone will try to use a crescent to undo it, rather than a socket or the correct-sized spanner, and round off the corners.

"If you haven't, definately take the carb top off and open up the vacuum passage. This makes a big difference in throttle response."

Err, have any more details about this mod?

Charles.

if you have a newer xt, dont worry about this mod. it has already been done. i have a 2004 and i didn't need to do that job. but i wish i could pop wheelies, but i can't. sob

I have an old (1987) TW200, which has the same carbureator. So I'm worried!

Charles.

I have the carb in pieces, sitting on the pool table, waiting for the UK carb mod. Wish me luck that the bike will run better....it HAS to. I'm doing the carb mod and this exhaust mod and the airbox mod. I have a 2006 and it has run like crap for all of it's 110 miles, never seen a new bike run worse. I'm sitting here reading about all the great results, the starting and power, and can't wait to get the bike together for the weekend. Thanks for all the info Jay, I haven't forgotten. Thank you guys for such an informative website. Hope this works out.

I finally did this mod, and I agree agree with those who say it makes the bike run with a little more power and a little louder.

The hardest part of the project was removing the end cap. A friend of mine who's an engineer with a lot of tools used a big pair of channel locks to grip the cap and wrench it free (after the screw was removed, of course).

Thanks for everyone who wrote about this mod. You provided me with the inspiration and confidence to proceed.

Just finished the MSS rider course and waiting to pick-up my lisc. Ihave been reading Greg's and Z1's posts for 6 weeks and just wanted to know if the 1 7/8" hole will be too noisy when I hit theforest preserve trails? If so can I get another slip-on SA for that purpose?

Hi meatball,

You might consider doing Z1's mod with the 1 7/8 hole saw, and just leave your stock spark arrestor alone.

If you do this, the bike isn't really that much louder than before... just more growl... and you still get to enjoy the increased performance while retaining the off road fire protection of the stock spark arrestor.

Take Care,


Greg

Yeah i`ve just brought one for the missus...& after reading this post I thought I better give this a try.
But it must be an Aussie thing, as mine is welded too

I might grab a second hand one to butcher rather than attack the original.

Cheers

Greg---Thanks for the reply. Sounds good. Purchased 1-1/2 metal hole saw-thats all the had at Homedepot,that or the 2" but from what you talked about thats exactly the size when taking into consideration the circumference of the saw. Hopefully I can get in there with a grinder. I also picked up some anti-seize. The bolts and screws only have 4miles on them so it should be perfect timing with the info I'm getting. Wondering what would be next after this project? The 16T road gearing you talked about, is that a set of 6 smaller gears that would replace the stock. I'm not sure how that would effect my bike on the trails?

[ May 24, 2006: Message edited by: meatball476 ]

[ May 24, 2006: Message edited by: meatball476 ]

Hi meatball,

A 1 1/2 holesaw should be just fine. I don't think it really makes that much difference if you ream it out any further.

The front sprocket is outside of the transmission, and is a single simple gear that drives the chain. You can change it very easily. Stock is 15T, dirt gearing is usually 14T, road gearing is 16T. If you're doing any dirt riding, don't go to the 16T. It's only useful if you are using your bike as a road transportation vehicle.

Take Care,


Greg

Greg

So the gear is visible then? I think for now, not being expierienced in my bike there is no need to worry about the gears. But I continue to learn. Are you happy with your pegs? The first ride I thought they felt small and last night I searched around and found I can buy extensions. I'm going to ask the shop I purchased my bike from if he knows bigger pegs that would fit. I read alot about the bearings. Where can I get sealed ones? I appreciate your input and probably will continue to pick your brain if you let me. Have a great weekend!!!

Another exhaust mod has been completed. 1987 TT225T. Took all of 5 minutes...

1 3/4" hole saw on a Milwalkee Magnum drillmotor with a 6" extension.

Noticeable improvement on throttle response and lowend - front end lifts easier. Increased noise level barely perceptible except on the overrun (popping when you throttle down).

Great tip... thanks to those that took the plunge initially.

Don in Nipomo

[ June 04, 2006: Message edited by: D.Bachtel ]

Hi meatball,

Yes, leave them be for now. The stock gears are the best all around compromise between dirt and street riding. The only reason to gear up would be if you never do any serious dirt riding.

The front sprocket is under an easily removeable plastic cover. Just follow your chain forward from the rear sprocket and there it is.



Hey, for larger pegs check out the ones on EBAY specifically for the XTs that go up for sale every weekend. They're beautiful works of manufacturing. I actually like the small pegs, because my feet aren't that long, and the larger ones would place my foot back too far from the shifter.



I don't know, but that subject has come up here before, and can be found in the past posts with the local search engine.



You too... I see riding in our weekend.

Glad to help out, so pick away... I pick everyone's brains here, too.

Take Care,


Greg

[ May 26, 2006: Message edited by: Greg ]

Hello Greg

Its Saturday eve and the hole in the muffler is completed. I had some fun taking the muffler off because the drill bit came off the hole saw and fell in. Then I made it through with the hole saw but couldn't retrieve the piece of metal and then realized it cut 95% of the metal and then bent in. I fished it out with a hanger with that wonderful drill hole I made in the piece of metal. Put 21 miles on my 7mile bike and it sounded great as well as response. I asked the guy at the dealer who introduced me to my new bike about drilling out the muffler that was reported on an internet site and he said," no, don't do that I can put an aftermarket exhaust on for you". Let's see, $23 for a drill ext. and a hole saw or $300 for an aftermarket--no brainer!!
Greg, if I install a fuel filter does it go on after the fuel cock?

[ May 27, 2006: Message edited by: meatball476 ]

Whooo Hooo! I performed this operation over the weekend on our '92 Serow, and all I can say is 'why did I wait so long on this?'

Thankfully, and somewhat unbelievably, after a couple blasts of WD40 the screw on the Spark Arrestor came out with little trouble. More difficult was getting the SA off, but I remembered reading somebody's suggestion of inserting a screwdriver into the hole that accesses said screw and tapping lightly to help un-lodge the SA, and that worked well. I bored out the 1 1/2 inch hole, fished out the left-over metal disk and shavings, reassembled the unit (I've left the fins on the SA alone for now--maybe I'll cut them down a bit later, but I don't think it's needed), and wow! Holy new-found throttle response, Batman!

And to think I was watching 3 different after-market systems on ebay: Big Gun, FMF and Pro Circuit all happened to be available recently. I figured I owed it to myself to get out there and do this mod first to check out these claimed results, and I'll be damned if it's not a new bike. I already had the Uni filter installed, which contributes more to the noise level than opening up this pipe. I'd say it's barely louder now than it was before uncorking it (but WITH the Uni installed--I'm sure it'd be perceived louder over stock pipe with stock air filter).

For me, there may be a couple more HP gained, but the real treat is the vastly improved throttle response--it's night and day. Thank you all for your guts to try this and your posts to help others avoid mistakes and delays. Oh yeah, and thanks for saving me at least $200+ bucks on an unnecessary aftermarket system. They may sound more 'tuned' than this mod, but they can't possibly perform significantly better than this to warrant (for me) the added expense. Now where did I see that posting about modding the snorkel...

Hey Spew,

I regularly swap back and forth between the modified stock exhaust and aftermarket ones, so this gives me a pretty good assessment of how they compare. Aftermarket exhausts are better, but their improvement is far less than the difference between a totally stock exhaust and a modified stock exhaust.

If this was expressed in numbers between 1 and 10... stock exhaust being 1... and aftermarket being 10...

...I'd put the Z1 modified stock exhaust at about a 7, which makes it extremely cost effective for the results received.

Take Care,


Greg

All -
Thanks for the inspiration. Like so many others, I have read, and read, and read. finally took action and did the Z1 thing to my 2003 XT. Great results! (same as everyone else and I'm thrilled). One question though:

How do I conduct the "spark plug test" and what am I looking for? I understand that this will tell me if I require mod's to the carb settings. BTW, I intend to reset the pilot jet screw to 3 turns.

Thanks for the feedback. You all should know that I'm hooked now!


Cheers,

I have a 2006 xt225 i just got saturday and today i took the end cap off the muffler and its open all the way down.

Brand new it only had 3 miles on it when i picked it up.

I should ad that the spark arrestor it is the same as the one in thi pick .

Hi foam,

It's actually Z1's Cheap and Easy mod... mine is replacing the stock spark arrestor with a 2 inch copper plumbing cap with a 3/4 inch hole in it.

And it's usually not a good idea to do two mods at the same time, because you won't know which mod is causing more of the problem, or if it is the sum of the two together.




Did you check inside the holesaw?

(sorry, couldn't resist)



It could seem to be backfiring more because now that the barrier has been removed, you can hear it... or it also could be backfiring more from the richer mixture of the needle shim. That's the problem with doing two mods at the same time. Your engine may not idle so good, if you open up your pilot screw more than three turns.




What does your spark plug look like? It will tell you if you need to richen up your mixture.

I've been running mine with the stock 40 and 125 jets, no shimmed needle, and three turns on the pilot screw with both modified stock and aftermarket exhausts for thousands of miles of easy starting and excellent mileage, and don't see any need to do anything to the carb.

Elevation might figure into the mix, as I'm basically at 1,000 feet, and don't ride any higher than about 3,000 feet, but going higher would richen up the mixture rather than lean it out.

Take Care,


Greg

Hey Z1 or Greg,

I don't have a 1 1/2" metal hole saw, I calculate that it would take (9) 1/2" holes to equal (1) 1 1/2" hole. What do you think about this approach ? I have removed the end-cap and it looks like there is enought area to drill that many smaller holes. Doing that might cause the baffle to rust out quicker ?

I would appreciate any thoughts on this before I proceed.

TEXASXT225 Wrote:

I personally would not drill a bunch of small holes in the inner end cap and then leave it that way, as you are dealing with an exhaust pulse that is better handled by one large hole rather than a bunch of small ones.

You could drill a bunch of small holes around the parimeter of the inner end cap right next to each other and then punch the plug out of there with a punch, so you end up with one big hole. Then if you wanted to you could use a small grinding wheel on the end of an extension, connected to a drill to smooth out the jagged hole left.

Better yet just save $15-$25 and go buy an extension and metal hole saw, or take the pipe off and go to a metal working shop and have them drill it out for you. It takes about 30 seconds with the proper hole saw, where the other route will take you an hour + to complete the job.

therocks wrote:

Did you shine a flashlight in the pipe so you could see down into it? The end cap is about 8-10 inches deep inside the pipe.

foamfollower

What year is your XT225? The reason I ask is that the later model XT's don't need the carb mods, or jetting changes as long as you are not riding in high altitudes.

My 2002 did not need any jetting changes other than turning the pilot screw out 3 turns. I did put a 130 main in it, but it made no real difference one way or the other, so I just decided to leave it in. I could have easily kept the stock 125 main in it though.

The Aussie end caps are welded on...

So i took it to work & got the fitters to cut the end cap of to do the mod to the baffle. BUT our baffles are a different set up, it has a series of 4 pipes before exiting the end cap. 2 pipes (15mm diameter) feed the exhaust gases into a chamber then out through another pipe (20mm diameter)then back through the final pipe (10mm diameter & about 100mm long)& out through the end cap.
No wonder it feels gutless, so what i`m getting the fitters to do, is make me another end cap that will bolt onto the muffler & bipass all the ins & outs of the baffle pipes. The gasses will still flow through the 2 15mm diameter pipe but exit straight out the end cap & not be forced through the other pipes.

Cheers

Well I got the muffler back today all rewelded with a removable end cap...

WHAT a difference it makes to the performance i`d say it FEELS like close to 40-50% increase, but in reality probally about 10-15%.

Thanks again for the tip

Cheers

Hi NOZ,

Good to hear that you found a practical workable solution. It's fascinating to watch how the ideas bounce around here!

Is there any chance you could post a pic or two of the removable cap. Now you got me all curious about the design of the cap and how it attaches.

Take Care,


Greg

G`day Greg

No probs about the pics...BUT i tried to post them but haven`t got a host site.I could email them to you if you like.

It`s very simple really, it`s just a ring welded to the muffler then the end cap bolts to it.

Cheers

There's a far easier way. Go here:

Photobucket

It's free, and very easy to use. You can upload your photos to your own online album, and each one has its own url (address), then you just copy and paste the address of the picture you want to show up here.


[IMG}http://i17.photobucket.com/albums/b90/compost_bin/serowblack6.jpg[/IMG]

This is what the address for the Photobucket picture looks like. I changed one character so that it would show up as script instead of the picture.

Take Care,


Greg

[ June 10, 2006: Message edited by: Greg ]

a big thanks for the exhaust info. combined with the carb mod, the bike really comes alive. sure beats spending $300 on aftermarket parts. having a blast my '06!!

Thanks Greg,

Here goes...just registered with Photobucket.




It worked..!!

The bottom pic is of the baffles, the gases come in through the two vertical pipes, then go back into the muffler throught the larger pipe to the left & then exit to the end cap through the TINY pipe.

Cheers

[ June 11, 2006: Message edited by: NOZ69 ]

Hi NOZ,

What a nice neat clean job. How does the bike run now?

Greg

G`day Greg,

I can`t believe the difference it made, either can the wife (her bike). It`s like a completley different bike.

I still haven`t played with the carby yet...doesn`t seem to have the brass plug for the pilot screw (bonus). The wife is at me for playing with her bike more than mine (mines powerful enough)& besides i`m a "tinkerer" & can`t help myself

Cheers

Hey guys,
I just installed my Big Gun EvoX exhaust system on my '06 xt225 and I love it. I didn't have to rejet and it seemed to have added the 3 to 4 horsepower that the manufacturer claimed that it would. It has more pull and sounds a lot better. It just took a fews minutes to install, but a little anti sieze at the coupling will make it easier to install. Well worth the money for sure. I also trimmed down the front fender and I am a lot happier with the look of that.
Just FYI,
Matt

Quick question on the SA. I washed the bike this afternoon, oiled and adjusted the chain and took the aircleaner filter out to clean.

Then I took off the spark arrestor to get an idea what was there. Anyway when I took the SA off it had some fluff in various places. Where did it come from? There is none of the engine side of the screen so it has to be somne kind of SA sealer I suppose.

There wasn't much there so I pulled it off.

The bike just turned over 2000 miles and I will be checking the tappet clearance next and of course doing the Z1 mod. Have to pick up the hole drill and extension.

Then next will be the 3 turn carb mod.

Fun so far.

Wade in NW Florida

Wow what an effective mod. I just did it on my 2003.
Now it's a serow on steroids. More grunt and it sings through all the gears. The pressure difference at the exit of the spark arrestor was really something. Instead of almost no pressure spikes; now little pulses come out you can feel with your hand back a foot of so. Maybe a little more noise but it is lower frequency noise.

I just registered so I could thank Z1 for formulating this mod and following through.

Russ in Calif.

3 turns out on the pilot and Z1's muffler mod. Still have the others to go.

I have done the Z1 mod (1.5 inch hole in baffle) and am thinking about moving to an aftermarket system, mostly because my neighbors complain the bike is loud after the drill out. I have called Pro Circuit, FMF, and Big Gun. According to these companies, the Pro Circuit with a quiet tip runs 98-99 db, the FMF 99, and the Big Gun Evo X with a silencer at 96 db.

Based on this, it looks like the Big Gun is the quietest of the available aftermarket systems, but you have to buy the complete system (header and silencer) so it is an arm and a leg.

My question is, does anyone know what the stock muffler db rating is, and, more importantly, roughly what the db rating is with the Z1 mod? I am not going to waste my money if the Big Gun is not going to be any quieter.

Any input would be appreciated!

cda888, based on what I read here, after doing the hole thing, putting the spark arrestor back in quiets it down. I plan to do the mod myself soon.

Thanks for the response. The problem is that even with the spark arrestor in, it is still significantly louder than stock. I don't think it is that bad but I guess for suburbia, it would be better if it was quieter.

I guess I hope an aftermarket pipe will do the trick. I have ridden a KLX250s with the Big Gun pipe, and it didn't sound ridiculously loud, although it was clearly louder than my then-stock XT. It did seem like there was more vibration though (both with Z1 mod and the Big Gun pipe).

The aftermarket pipe will be louder than your stocker, even with the stocker mod. When I did my mod on my stock pipe, it wasn't that much louder than stock, but it had a deeper growl. Then I went to an aftermarket exhaust made by Cobra (which they don't make anymore), and it's louder than my stocker with the mod.

As far as aftermarket pipes go, the FMF is pretty loud. Most on here that have had it, sell it. Those that have kept it, have packed it with silencer material.

With the Big Gun, you can get it with just the pipe, you don't have to buy the complete system (unless they changed things). The Pro Circuit is also a good pipe, but by your rating, is louder than the Big Gun.

Click the link (Sound Clips) , and you can hear the difference between my modded stocker and my Cobra exhaust....

Thanks for the reply- that actually helps a lot. I can see what people mean by saying the aftermarket pipes sound more "tuned-" seems a little smoother/deeper exhaust tone on acceleration.

I don't know what the noise db is on the Z1 mod stock exhaust, but I know it is more quiet than the after market exhausts you are looking into. Why not just keep the revs down until you are a few blocks away? If you keep the revs down the modified exhaust is just a bit louder than stock, but not by much as long as you are still running the spark arrester in it. If you really need to quiet the exhaust back down from the mod, all you need to do is measure the distance in to where the plate/baffle was that you drilled out of the exhaust. If it is 8-inches in from the end of the pipe, then take your spark arrester to a welding shop and have them extend the end of the spark arrester to match the distance in where the baffle use to be that you drilled through, and have them weld a metal disc at the end of the extended spark arrester to match the same size diameter hole that you drilled through the baffle. The extended spark arrester will now act in the same way the stock plate/baffle did, to redirect the exhaust around it.

I also posted this under wrenching, but wanted to be sure everyone knows how great this mod is!!


Got a set of the craftsman stuck bolt extractors-#3 was the right one. It grabbed real well- too bad the bolt was frozen and it snapped off. Of course not flush enough with the pipe to allow me to get the SA off. Ended up boogering (is that really a word?)the hole in the re-enforced plate in the muffler, but I got the SA off finally. FWIW, the '06's are same as the rest-at least in California.

Decided to continue with the Z1 mod. Got the 1 1/2" bi-metal hole saw and a 12" bit extension. Started 1st pilot hole too high, but realized it and started a new one in the middle of the block off plate. Proceeded to cut out the disc, which then fell forward into the pipe. DAMN! It took forever to fish it out-I thought I was going to have to take the muffler off and shake it out to where I could reach it. Finally using an aluminum angle to prevent the magnet from sticking to the side of the pipe, I was able to get the disc up into the hole I had drilled, but of course I dropped it back into the pipe. After a long tedious time, I was able to retrieve it again, but this time I hooked it with a bent clothes hanger and was able to pull it out. I then used the magnet to pick up any residual shavings that I didn't get on my previous attempts to retrieve the disc. Then hooked up the vacuum to suck out anything left in the pipe.

I rotated the SA @ 5-7* counter-clockwise and drilled a new hole in the re-enforcing plate. I tapped it for a 5/16-18 socket head bolt and re-installed the SA. Blue loc-tite on the bolt, anti-seize where the SA joins the muff and pipe.

Several beers later, it's all back together and guess what? this is a totally different bike- 1st gear is useful & actually romps! Doesn't sound like a Vespa anymore. On the flat, it jumps to 65 MPH (I weigh 230#)without hesitation. I didn't try any faster since it still has so few miles on it.

This bike is gonna be fun!!!!!!!!!!!!!!

Thanks Z1!!
_________________________
Which is more fun-the XT in the dirt or the XL in the twisties?

This is why I took my pipe off and then did the mod. I like to take extra precaution....

Just finished the mod myself. My bike is a 06 with about 3000 miles. The spark arrestor bolt of course stripped out. I ended up finding an impact driver at a local hardware store for $13 and that did the trick. The end cap slid right out and I was able to drill through the block-off cap without my fanfare. Fished the drop out with a manget. I did all of this with the muffler off the bike. Considering it takes all of about 2 minutes to remove it, I consider this well worth the effort.

At the same time I cut open the airbox, added an Uni and rejetted to a 130 main. The bike definitely has more power, but I'm still wanting a lot more. I've been riding my father-in-law's modded XR400 & KTM 300 2-stroke too much lately.

this is my bookmark post - ill be doing this soon!

I did the drill-out mod to my new 07. It definitely helps. For you noise conscious guys, I noticed that with a 3/4 hole the noise was just like stock. Then I went to 1 1/8" hole and it got a good bit louder. So if you want some gains but no noise, I'd recommend you stay at 3/4" max.
Hint: I let the bike idle while I was drilling (cough,cough), and it blew all the shavings out in my face. Just wear glasses and be careful and its a good way to keep the shavings from falling back into the muffler body.
Another hint: I used a Unibit, and it works much better than a hole saw.
STJ

well, after damn near a year of studying these threads I decided to get to it. pulled out the snorkel and WOW that made a huuuge difference! I can actually use 2nd on the street now!! Usually I was in 3rd goin on 4th by the time I crossed an intersection from a stop.
so anywho, after soaking the screw (which had been completely and totally stripped out by the previous owner) with PB blaster numerous times and heating it and tapping it with screwdriver/hammer and repeating, I moved on to the extractor bit, which I will NEVER make that mistake again.
so I started trying to use the grinder to make a slot for a flathead, that didnt turn out so well.
now I have gored the exhaust with the grinder to the point that nothing but rust is holding it on. and man, is it holding on. any suggestions to get it out? Ill be damned if I got this far just to have a lil rust stop me. Ive been ridin hard over bumpy stuff, gettin the pipes really hot and tryin to get it off then, and nothing will budge it. It is a '95, and has been mistreated most of its life so its no surprise that theres some serious rust goin on, but man. its personal now.

Riding the bike hard probably won't heat anything up enough to help with breaking the rust free. Keep soaking that inner flange of the tip extension with PJ1. Propane torch on the inner flange. Use a rubber mallot on the tip extension and just work things around until it loosens up. If you've got a small slide hammer with a large hook, that'll help too. Be patient.

Remember though, if you do the Z1 exhaust mod, be prepared to re-jet the carburetor.

-Steve

Here's the trick I use: Put a 1/2" wooden dowel into the screw cavity with the dowel pointing sharply toward the front of the bike. Now hit the dowel with a hammer which will tend to knock the spark arrestor out. Good luck.
STJ

I have done the Exhaust Mod but I am going for a ride in an area this weekend that has Strict Exhaust Noise Laws, 1. does anyone know what the DB is with the Mod? 2. Does anyone tried stuffing exhaust packing in the pipe or around the spark arrester and tested it? I want to take the XT225 but its a long trip to get told I can not ride the bike or get a nice fat Ticket..

Duck

I don't know the DB level, but your XT will not be any louder than any legal 2 stroke, stock WR250, XR400. Your XT probably has more airbox noise than exhaust noise.

Wrapping the spark arrestor will quiet things down a bit, but at the cost of some power loss.

-Steve

Most State Parks have a db level somewhere between 93-96 db's if I remember correctly. I don't think the modded stock exhaust even comes close to that. You may be able to go online to find out what the legal db level is for where you are riding....

Duck, Where will you be riding?

-Steve

Riding in the Cle Elum area Sat and Sun. If you want to join us send me a PM.

The WA State law for db Level is 105db, I got a cheap sound meter from Radio Shack and tested the db on the Stock 08 XT250 it was 78db at idle and 96 at half throttle or more. The 05 XT225 with the exhaust mod was 82 at idle and 98-100 at half throttle. Adding muffler packing only changes the db at idle to about 79-80db.

Duck

Hey Duck, thanx for throwing out the numbers.

105DB huh? The neat thing about the Z1 exhaust mod is that visually it appears 100% stock. Where as, my buddy has an XT600 with a Super Trap muffler with the adjustable disks.. Well, we got it adjusted for optimal performance all right.

Two words...

Friggin LOUD!

For a dual purpose thumper.

Our XT's won't even get a second look by the policia.

-Steve

thanks for the tips jack an john

ill try to be patient. I guess thatll give me time to find some jets.

I was under the impression that us folks at sea level may not have the same issues, but we'll see.

jack, have you done the 3 turns out thing?

Does anyone have a link handy to buy one of those Cobra or XT 225 After market exhaust? Getting Parts in Australia is hard

Cheers all

Makes me wish I had time to go to the Cle Elum area with Duck last weekend. Trail riding at it's best.

Yes, I have done the 3 turns out thing... Actually four seems to be where my engine runs best.

-Steve

The Cobra exhaust is no longer available for the XT225. They still make some for ATV's and Cruiser bikes. For an aftermarket exhaust, you can get a Big Gun, Pro Circuit, or FMF. Look up the ones made for a 2004 TTR225....

ok,
I did this mod ( 1.5" hole)

it IS stronger, it IS louder.

but its surging on the idle circuit.

Ive drilled and removed the low jet plug, and I recall setting it to 3.0 turns out.

how many turns out can I go before the adjustment becomes ineffective?

and what is the vacuum tube mod, or the UK carb mod?

bike is a 2000, manufacturer date 1999...

I would not go passed 3.5 turns to 4 turns at the very most. Have you re-jetted your carb, or just did the "3-turn" mod? If you have not re-jetted, you might try going up a step to the 42.5 pilot jet, or shimming your needle....

bike is totally stock, except that I removed that pilot screw adjustor cap, and turned it to 3 turns, and then cut a 1.5 inch hole into the muffler as per the z1 mod.

Ive read thru these 16 pages and most folks that changed to the 42.5 pilot jet, ended up swapping BACK to the 40 size.

I might shim the needle, although, that too ive read here, was done and re-done.

typical of my mods, they never quite work out like everyone else mods do.

I once knocked the baffles out of a honda shadow, and it was then too lean to run, it sat in the garage for a week until I got a dyna-jet kit in the mail.

So who has done this on a new 250? I am in the process if trying to get it done and I am running into a few hickups.I bought an extension that won't fit in my drill and I bought a metal hole saw that wont fit in my extension. SOOO.... I am going to buy the biggest longest bit I can and then use a tapered bit to grind out the hole lie z1 did. Do I need to woory about the shavings or are those going to blast out the end like I am hoping they will? Thanks!

I took my pipe off the bike to do this. I didn't want to take any chance of getting shavings doing any harm....

I didn't take mine off but the drilled out piece fell inside after it cut through so I ended up taking it off anyway. In hindsight, after seeing how easy it was to take off and put back on, I would have taken it off in the first place.

Well, I got impatient with my project, and bought a long drill bit drilled several holes in a circle on the baffel. Tonight I am going to pop the piece out and grind the circle to a nice looking circle. I started it up, and with a roar a shower of small metal came out like fireworks on the fourth of July. It sounds mean with the SA out and my neighbor with a VRod even turned around and looked as he was polishing his V-twin and gave an aproving nod. I also installed some after market turn signals, I am next installing an Acerbis Cyclops head light, and then more to come after that.....I am working towards my genre of a bike "supermoto/dirt racer". Man not much better than tinkering and making the bike you want to ride.

I just did the exhaust mod on the wife’s 08 XT250. It really improved the acceleration and the bike can now pull easily up to and past 80 mph. The bike is a bit louder while on the gas, but not too load, as I am not into the loud pipe stuff.

I took the end cap off, using an impact wrench which will ensure you get the screw loose and will not strip the Phillips head. A bit of liquid wrench to loosen the cap, then wiggle the end cap off. You can also insert a large screw driver into the hole which allows access to the Phillips screw….and use a small block of wood to pry against…..and the end cap will pop right off.

Next look down the pipe and about 8 inches down….you will see the plate at the end of the cylinder inside the pipe that is blocking the exhaust flow. Some folks drill a few holes in it, but I used a 1 7/8th inch hole drill bit and removed the entire plate. Then just put the end cap back on and the mod is done.

Also, I took the plastic cover off of the top of the air box that holds the filter in. I fabricated a small length of aluminum to hold the filter in and used the existing screw to secure the plate to the air box.

I can’t provide photos now as am out of town.

Is the bike still running well, does it seem to need to be rejetted? Curious yet nervous at opening my 09 up without the availability of the pilot jet.

We did my father's '09 Tuesday night, along with making an additional hole in the airbox lid (dremeled a similar-sized hole right beside the stock hole.) It sure is a lot louder. He says it's stronger, but I haven't ridden it yet to get my take on it.

Why is the pilot jet unavailable? I thought I read on here (somewhere) that the small Mikuni jets fit this carb (even though it isn't a Mikuni carb.)

I did this to my 2009 and have never looked back. Felt upgrade in seat of pants, but never checked further. Not too noticeably louder after the mod. With screw turned 3 times, not running lean as it was prior and definitely would have been after the mod. Good luck to whoever reads this next!

http://4strokes.com/tech/yamaha/xt250_exh_uncork/
http://www.4strokes.com/forums/topic.asp?TOPIC_ID=30344

Hi Guys n Gals,

don't forget that the US spec XT250 has a different exhaust when compared with the japan spec model.

I recently purchased a 2006 XT225, bone stock except for a 16 tooth countershaft sprocket. It will be ridden mostly ~1500-2000 feet elevation.

After reading all 17 pages of this topic, plus all 11 pages of Z1's super duper stock exhaust mod, I have decided to start with a step drill bit, with a 1" hole, and increasing to a 127.5 main jet. I haven't decided whether or not to raise the carb needle.

Since it starts easily, I'm not planning to change the pilot jet. I also don't plan to remove the air snorkel, at least not immediately. Is there any difference in rider-perceived noise without the snorkel, vs drilling holes in the side of the air box?

I needed a heat gun to remove the two bolts that hold the muffler to the frame, but Liquid Wrench for 24 hours+ heat gun was not enough to remove the screw that holds the spark arrester in place, so as so many others have done, I stripped the screw, then drilled it out, and will retap the hole, then replace with a socket head screw. I have read at least one comment that said not to use stainless, and I'm wondering why. While the muffler is off, I plan to repaint it with UHT paint.

Since so many people have been down this road already, I'm just asking for feedback about this plan of action, aware that I can always make a small hole bigger, but I can't make a large hole smaller.

#127.5 main jet...no shims on the jet-needle...stock #40 pilot jet, 3-turn Pilot Jet Adjustment Screw, with your Z1 mod at 1" hole size.

This should be ideal at those altitudes, IF YOUR FLOAT HEIGHTS ARE WITHIN SPECS.

Pulling the snorkel adds a bit more response; some people however feel that this causes noise. I've never noticed it (with the Z1 mod probably loud enough to drown it out).

Alexd

Right — I forgot about 3 turns out for the pilot screw.

Since I already had everything apart, I removed the carb, and drilling out the plug was easy, although I don't understand why they put the pilot screw at the bottom of the carburetor. Before I read up on the procedure, I thought it was in a little opening on the left side — glad I didn't try drilling that out!

After I pulled the plug, I found that the pilot screw was only ~1/8 turn out, which seems to be pretty common for the 2006 model — I'm amazed the previous owner thought it ran just fine. Since it was already working pretty well, I backed the screw out to just 1 turn, rather than three. Plenty of time for experimentation.

On many motorcycles, Pilot jet (and similar) adjustments have large effects. That's not true on our later carbed XT225s.
I've found virtually no reason to change the setting from 3 TURNS OUT at either Sea Level or 13,000' That's partially true because of the design, and also that at several turns out, the limiting fuel factor is the Pilot jet number itself.

Experimentation is fun...but you will find that 2-1/2 to 3 turns out is perfect for starting/warm-up/small throttle response.

Alexd

Too bad this thread didn't continue into the FI models of the XT250. I would have been real interested in what would have been the end ( if there is such a thing ) You guys did an
incredible amount of fiddling, experimenting and modifying the exhaust. It's too bad there isn't nearly the interest now a days especially since there are all kinds of alternative China
mufflers that look like carbon fiber in different lengths. At $ 50 and under it's real tempting. As long as it wouldn't lose power I'd be happy with the 6 lbs or so weight loss up high on
the bike, better CG that might even be noticeable.. Bravo to all you guys for 17 pages of interesting reading..

I did this mod just to make my XT actually sound like a dirt bike. Despite rejetting the carburetor a few times, I never got any perceptible performance increase. It may sound faster, but that is just an illusion. A stock XT225 makes less than 20hp. even if you increased it by 10%, which is probably not possible without ruining it's reliability, it wouldn't be enough to really notice. Doing this mod on an EFI bike would likely just mess things up. Decreasing backpressure always results in a leaner mixture. And to change the mixture on an EFI setup you need a $500 electronic tuner. A big part of why I like the XT225 is BECAUSE it is carbureted. It is something pretty much any mechanically inclined person can work on without a lot of expensive electronic equipment. I have 6 bikes, ALL of them are carbureted. If you want more power, you're better off just getting a bigger bike. The Yamaha WR250R makes 30hp stock. That's 33% more than what the XT makes. That's the way to go if you want more power out of a lightweight small displacement dual sport. Problem is (for me anyway) the seat is 6" higher. I couldn't even get on it. And all I do is light trail riding anyway.

I believe the 250's exhaust is different such that it's not as simple as just drilling a bigger hole in a baffle. I'd love to find someone's junk stock exhaust and cut it in half to see what it looks like inside.

You're right about the 250's exhaust being different. I took the end cap of my XT250 thinking I'd see if something like the Z1 mod we do on the 225s might work. Granted I didn't go further than that, but with the end cap out of the way the visible inside of the muffler was nothing at all like the exhaust system on the XT225. There's no obvious way to drill things out in there and come up with something that works like the Z1 does on the 225...