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WR250F Top end sputter?

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I bought a used, excellent condition, 2009 WR250F last Saturday. It has all the free mods done and a FMF Powercore 4 slip-on muffler. Supposedly, it has been "properly" jetted. I don't think so, because at lower speeds it runs fine, but when approaching WOT under acceleration it begins to sputter....way before the rev limiter should kick in. Anyway, I have searched and found it may be a overly rich condition called "four stroking". I am waiting on the JD Jet kit. I feel certain proper jetting will cure the problem, but wanted to know if I am on the right track. I called JD and only get voice mail. Ideas/suggestions appreciated.

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Not four stroking, it is eight stroking, though it can do that being lean too.

If the problem is worse in 1st and 2nd and lest pronouced in the higher gears, it probably is too rich on the needle taper.

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Misses at WOT are probably main jet, if you are not hitting the rev limiter. The recommendations of the JD kit should get you close and improve the wide open throttle response. Sometimes POs put in the biggest main they read about, without consideration of altitude, temp, exhaust, cam, etc differences. When I bought my used WR250F, it was stupid rich.

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I bought a used, excellent condition, 2009 WR250F last Saturday. It has all the free mods done and a FMF Powercore 4 slip-on muffler. Supposedly, it has been "properly" jetted. I don't think so, because at lower speeds it runs fine, but when approaching WOT under acceleration it begins to sputter....way before the rev limiter should kick in. Anyway, I have searched and found it may be a overly rich condition called "four stroking". I am waiting on the JD Jet kit. I feel certain proper jetting will cure the problem, but wanted to know if I am on the right track. I called JD and only get voice mail. Ideas/suggestions appreciated.

what's the current jetting?

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I do not know how it is jetted yet. I was waiting until my JD Jet kit arrives before I pulled it out to check. I feel certain that proper jetting is the solution.

Talked to Dave today and he agrees that the main jet is too large and the needle is too high. His kit should make a world of difference. Thanks for the replies and advice!

Edited by Kickngas

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WooHoo!! JD Jetting kit did the trick. May have to experiment with the main jet size, but for now, it runs great. Went with a 185 main and a 50 leak jet, red needle 4th slot. Added the thick "O" ring. I am going to get a new plug tomorrow so I can check how it is burning from this base setup. Stuttering is definitely gone. Opened it up to a whopping 82 mph. I probably need to check if the tire diameter has been set correctly because 82 sounds pretty high.

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I cleaned the filter first thing, so that was not the issue. I do have a No-Toil in now that should give better air flow. New plug should be here tomorrow, so then I can check how rich or lean it is running.

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Hey mate,

ive got a yz 250f 2008 and 2011 and they both spluter when there cold you have to let them get hot before floging them this has not happend with any other bike ive owned and they both have stock pipes.... my mates has a arqapovic and another with DRD they both it to it is just a thing with them i geuss.

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Ox,

Sputtering happened when warm/hot, not just at cold start. The JD Jetting kit did the trick though. Now I have a slight bog on initial throttle wap, so I may go down a size on my main jet to fix that issue. Runs like a scalded dog on top end now!!

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