Hello, I have a 2008 KX250F with a 290 big bore kit. The bike ran exceptional all season until late in the season. Now, whenever I start the bike it idles extremely high most of the time. it acts like it has a mind of its own. sometimes it will idle somewhat normal, others it will idle very high. For instance, I will be riding on the track and will go into a corner, and the bike will act as it has cruise control?? it just keeps going like im still giving it some throttle. but, as soon as I pull the clutch in, the bike wants to die. also, im not sure if it will help you guys diagnose the problem, but whenever I let off the throttle, the bike backfires and pops pretty often. If you could send some help to diagnose this, it would be greatly appreciated!

 

but it is still easy to start?

First thing that I would do is check the carb and boot. For leaks or gunk in the carb.

this is a big bore, so a leak down or a compression test. What are the numbers? Are there any leakage signs around the cyl head, base gaskets?

Pictures of the project are always cool to see.

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