Jump to content
Sign in to follow this  

03 WR250F Jetting

Recommended Posts

Did a search on this and didn't get any good hits on this, although I'm sure this has been covered before.

Stock 03 WR250F, GTYR exhaust insert with the three tubes removed, Airbox stock for now. PJ 42, MJ 185, Needle stock on 4th clip (stock pos). 800 Ft altitude, 50 to 65 Deg. F.

Had the classic too lean PJ (40). I had to run the fuel screw > 2 1/2 turns out to get it to run right just off of idle steady state and resolve the hanging Idle problem when new. Throttle response wasn't too bad. Increased PJ to a 42 which improved the way it ran steady state just off of idle with Fuel Screw about 2 turns out. Now it seems to have a worse hesitation when accelerating. Acts like it needs to clean out and is down on power during the transition. I think I've created an over-rich condition just off idle. Also considering opening up the airbox. What is everybody running for jets with stock and modified airbox.

BTW just installed a JD Jetting kit on my Son's YZF450. Huge improvement over stock jetting. If I could get my WR250 to run that good I'd be thrilled, but Iv'e spend my play money for the month.

Thanks All

Share this post


Link to post
Share on other sites

I had the same experience with the pilot jet and found the 42 made it run steady, as did you.

To fix the off-idl hesitation, you will probably end up having to work with the leak jet. First though, try raising your clip position one to see if that helps. Try to get your fuel screw as lean as possible and make sure your idle speed is set up around 2000 RPM.

That should help some, but if not, put it back where you've got it and check out www.thumperfaq.com/ap.htm for info on tuning the leak jet.

I haven't taken the tubes off of my GYT-R tip, but have opened my air box. I am also running the JD jetting kit, so my jet settings probably won't apply to your situation. IMHO it looks like you main is pretty rich. I'd think a 175 or 178 would be more suited to your current set up.

Have you modified your throttle stop and cut the grey wire?

Share this post


Link to post
Share on other sites

Thanks for the reply barton.

My main jet is stock, which I thought was 185 per the manual, but I may have confused the Non-USA spec. I forgot to mention the grey wire mod. I have not tried that yet. Iv'e heard both stories on that. Some people say they didn't notice a difference and others say they did. What was your experience? As I understand the mod, it changes the timming map to YZ spec. I did cut the throttle stop. I also forgot to mention that I did remove the airbox inlet or snorkel plug. I liked the results when I removed the three pipes out of the GYT-R insert. It's a little louder, (not offensive) but not as loud as no insert at all.

Share this post


Link to post
Share on other sites

I was pleasantly surprised when I removed the grey wire. It does nothing for bottom end, but WHOA! it really woke the mid range and top end up. It's a pretty quick fix, and if you use a small screw driver to tease it out of the plastic plug it is part of, you can easily plug it back in if you don't like it. I've never heard of anyone who didn't like it. Free horsepower.

Yeah, mine came with a 185 main jet stock too, and it was pretty rich. I didn't know ANYTHING about jetting at the time, but with a little reading and asking here, I was able to figure it out. Enough to be dangerous anyway. If you can find a place where you can get to full throttle UNDER LOAD (a muddy field is perfect, should be plenty of those around depending where you are in IN), you find the power is kind of muddy (sluggish and not snappy) at the top end. Then switch over to about a 178 main, and you should really feel the difference.

I just bought a YZF exhaust on line, so I'm gonna try that next. If it's too loud, maybe I'll go back to the WRF exhaust and cut the three pipes off of the GYT-R tip. Thanks for the "tip" (groan :crazy:BOO-O-O!hssss).

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×