2003 yz250f wont start

I just picked this bike up from my nephew, it had been sitting for awhile but supposedly ran about a month ago. I drained the gas and put fresh gas in and the bike fired after a lot of kicks. It did not run well, would not idle correctly so i removed the carb to make sure everything was cleaned and no jets where plugged. reassembled the carb, put it back in the bike and now it wont start. I put a new plug in it thinking maybe that was it but nothing.


So the bike went from running like crap to not running at all. I dont understand what the problem is?

Could still be carb. Take pilot jet out and soak in carb cleaner.

Could be low compression. Rings might be jammed in piston groove.

Could be slide stuck wide open in carb.

Went through the carb again this morning and i think i must have done a better job today as now the bike runs.



Bike now starts and runs but is real sensitive to idle adjustments, it either wants to die or the rpm's are too high. when the throttle is blipped the rmp's hang for a couple of seconds before dropping back down. Is this a valve issue or a tps issue. I havent checked the valves yet so that may be part of the issue.

Sounds like an air leak or badly adjusted fuel screw. Hanging idle is from a slightly lean condition.

Set your fuel screw:

With the bike warm and at a smooth slightly increased idle, get a small flat screwdriver  and slowly wind the fuel screw (out or in) until the RPM gets to its highest. Then screw the idle out to get the idle as low as possible but still smooth.



If you get to more than 3 full turns out , or end up less than 1/2 turn from bottoming the fuel screw, it means you either need a smaller pilot jet  or larger pilot jet .


Once you get the sweet spot for the fuel screw it will idle well without the hanging revs.

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