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