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...