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yz250f hard start after rebuild

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before the rebuild i could start this bike with two kicks when it was cold, now it takes me forever to start it and it wont idle worth a damn. all i replaced was the piston, cylinder, and clutch. the timing was dead on when i put it all back together. never touched the valves. but i just pulled the spark plug out and its very brown, (to much oil i think) what do you guys think i should do? or check?

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Leak down test to check that you put all of your gaskets are sealing properly

Try a larger pilot....

Hows it ruin once it starts?

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You know, I'm going through the same thing right now. I just got through a new top end, and had some similar issues, but I think I'm getting it resolved. In my situation, I think it's jetting. Previous to my new top end, I couldn't even touch the throttle when I kicked it. After the new top end, I actually have to give it a little throttle when I kick it. When I do, it usually starts within 2 kicks. Every 4 stroke I've owned has had little "starting tricks". After the new top end, it's kind of like I'm learning the bike all over again.

I also replaced the pilot jet and fuel screw. That seemed to help some.

Good luck.

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I just got back from the track (1st time out since the top end). I put a 45 pilot jet in mine with an aftermarket fuel screw. Ran decent, but I think I have a little more work to do with the fuel screw.

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