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XL 250r mid rev misfire when hot

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Hi All. Have a XL250r single carb. The problem is as follows .... starts fine runs fine until about of an hour of riding, it starts to miss at low revs (above idle approx 1500rpm)  wont pull. Stop the bike and it idles fine and revs out fine but if from idle you slowly rev it up it hits this area where is runs hard , miss fires and does a sharp crack of a back fire. Turn the bike off and starts with half a kick. If bike cools the gremling goes away but back after an hour. I fitted new coil, wire and plug. Any help appreciated 

 

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I had an 87 250x quad that would do the same thing. I can't remember if it was the coil or rectifier that went bad.( sorry it's been a few years)

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On some of the older bikes the needle jet in the Kehin carbs wears to an oval shape.  This causes a rich condition throughout the entire midrange.  My buddy's 1997 XR250 used to be a complete pan in the A$$ when it got hot.  Hard to start, misfires, backfires, flameouts, etc.  Once I replaced the worn needle jet the bike ran perfectly fine.  The next time you have the carb apart be sure to check it out.

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The reason I'm saying coil. Is that sometimes when could go out. When the get hot they fail. Then cool down work good. I'm not sure if there's a way to test under load. Maybe when it does it again check it with a volt meter while it's hot. Or if u have a donor coil check it

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Hi All. have had other suggest carb .  About 2 weeks ago when it would do it id have no spark so then fitted new coil n cap etc, now still does it but will re start and idle plus rev up, just miss is still there at that low rev .... will keep tickering with the easy things. cheers

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Well .... cleaned carb, new plug, cleaner air cleaner and still have prob. played with it more and seems to backfire almost out of time as in pop and chuff through air cleaner, and when you go to restart sometimes kicks back !!! cdi?????

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I had an 87 250x quad that would do the same thing. I can't remember if it was the coil or rectifier that went bad.( sorry it's been a few years)

I think it was CDI box, I know I replaced it but couldn't remember what issues I was having to make me swap it. I think it was dying when It got hot.

Long live the Thumper..... Brrrraaaappppp!

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