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Need help kx250f!!!

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I just bought a 2007 kx250f. It starts first kick with the choke on. Once you take the choke off it backfires and pops when letting off the gas and doesn't want to idle. Flames are also coming out of the pipe at night. The oil looks a little milky when running threw the glass on the clutch cover. I checked the valves one intake and one exahst were .001" tighter then spec calls. Also thier are 2 marks on the fly wheel witch one do I line up? The coolant does bubble in the radiater when running.

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Update. I lined up the second fly wheel mark the cam spockets lined up with the case with 28 pins between them the 28th being right on the cam mark. On the lobe side the marks are not even wither the case is it posiable for the cam to be bent? Causing all this?

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i took apart my carb tonight and found the accelerator pump diaphragm was torn could this be causing the popping on decel?

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I'm interested in this as well....Bought an 07 kx250f last year for a steal and love it but I do have a few slight problems with backfiring on deceleration and getting it started....usually takes me several kicks with the choke to fire it up...then it will cut off two or three times before it actually idles on its on....once its warm though it seems to run great...idles just fine and usually only takes a kick or two to restart....I'm pretty new to the four strokes now days...was a two stroker for years...been out of the game for about 7 years...got back into to ride with my son who's 8....don't know much about the valve clearance or when the last time it was checked...guess I need to get on that first...maybe play around with jets??

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i don't know much about the kx engine but backfiring is usually caused by running lean or the timing being off. the problems at idle sound like its running lean. and the over heating could be from letting it sit at idle to long or running overly lean these bikes are not meant to sit if there not moving they overheat almost instantly. i would start by checking the jetting and cleaning the carb along with fixing the accelerator pump i think that would be the best place to start and change the oil.

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All KX250f's need a richer pilot jet (a 42 vs, a 40). That will help with the popping. Also, installing an externally adjustable fuel screw is advisable. Popping should disappear if all other things are normal. Definitely replace the accelerator pump diaphragm! That would cause serious bogging. While you are in there doing that, go down one size on the power jet for more fuel shot (50 vs. a 55) from the pump. Throttle response goes way up! As stated, change the oil asap. If it continues to be milky you either have a blown head gasket or a leaky oil seal (my bet is on the head gasket, especially if it is overheating).

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I just read about the bubbling in the rad! Definitely a blown head gasket. Replace it immediately.

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