i have a 1993 yz250 that i been working on for a bit now it has a 45 pilot jet 360 main and it will only bumpstart and runs really ruff, when u give it full throttle it just smokes and won’t rev out and then when i let of i can never get it to idle proper and it starts hanging idling super high and just overall won’t run consistently or good was wondering if anyone would have be able to help
That jetting sounds incorrect. Is it running the stock carb? If so, stock jetting is 50 pilot and 178 main. Probably not getting enough fuel to idle and way too much afterwards.
The fast idle is probably a combo of being too lean and an air leak. Other than what’s been said, check the rubber intake to make sure it’s sealed and not cracked anywhere. You said it has a new top end; a leaky base gasket on the cylinder can cause the issue. I replaced the piston on one of my CR500s and some how the new base gasket got torn on reassembly - didn’t notice until I was at the track.
The fast idle is probably a combo of being too lean and an air leak. Other than what’s been said, check the rubber intake to make sure it’s sealed and not cracked anywhere. You said it has a new top end; a leaky base gasket on the cylinder can cause the issue. I replaced the piston on one of my CR500s and some how the new base gasket got torn on reassembly - didn’t notice until I was at the track.
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