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yz250f rebuild help

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hey guys. I bought my 02 yz250f 10 years ago. It was bored out when I bought it to a 280(79.95 mm piston) power bomb header and fmf exhaust. its been a good bike till a bolt holding on a oil hose by the right foot peg came loose and blew up. I bought a cylinder works high compression standard bore kit to put in it. the build went pretty good, made extra sure I had the timing right. Bolted it all back together and noticed right away it didn't have the compression I thought it should have. I have been reading other posted and I found one where a guy had a shim in cockeyed so the valve was stuck open. I checked for that and found my middle intake valve had just that. Fixed that and put it back together. Flipped the choke on and kicked it a few times and it took off. Seemed to idle good and the throttle response seemed normal. Figured I had it good to go but when I turn the choke off it runs like hell. throttle response seems off and wont run for long. I don't have the correct feeler gauges to go as small as they recommend but i can fit a .102mm under the 4 valves I can reach( I cant get at the middle intake one). Bike ran perfect when it blew so I'm kind of stumped. Would the size change make a difference? any help would be appreciated 

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hey guys. I bought my 02 yz250f 10 years ago. It was bored out when I bought it to a 280(79.95 mm piston) power bomb header and fmf exhaust. its been a good bike till a bolt holding on a oil hose by the right foot peg came loose and blew up. I bought a cylinder works high compression standard bore kit to put in it. the build went pretty good, made extra sure I had the timing right. Bolted it all back together and noticed right away it didn't have the compression I thought it should have. I have been reading other posted and I found one where a guy had a shim in cockeyed so the valve was stuck open. I checked for that and found my middle intake valve had just that. Fixed that and put it back together. Flipped the choke on and kicked it a few times and it took off. Seemed to idle good and the throttle response seemed normal. Figured I had it good to go but when I turn the choke off it runs like hell. throttle response seems off and wont run for long. I don't have the correct feeler gauges to go as small as they recommend but i can fit a .102mm under the 4 valves I can reach( I cant get at the middle intake one). Bike ran perfect when it blew so I'm kind of stumped. Would the size change make a difference? any help would be appreciated 

Kind of a classic sign of running lean.  Maybe the displacement change, changed your jetting that much? You try and dial in your fuel screw setting?

Maybe an air leak somewhere past the carb making it go lean? Check the plug to see what color it is?

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I haven't messed with the carb at all. The plug is black but I never did buy a new one when I did the top end. It actually smelt a bit gassy.  I did find a bit smaller feeler gauges. I can fit a .038 mm under all the lobes so one cant be opened a bit. One weird thing that happened when I put it back together is the choke stuck on the carb. Had to knock it with a wrench to stop the gas. Everything is starting to point at the carb but its just weird that it would be acting up now. It did sit for 6 months or so before I did this though.

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To me it looks like it sat with 10% ethanol gas in the carb. That was the problem with my bike. You will need to rebuild the whole carb. The ethanol dissolves everything. Even the metal gets eaten up. In the future, if possible buy ethanol free gas.

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I swapped the 185 main jet that was in it back to a factory 178 and put a brand new plug in. Turned the fuel screw all the way in and backed it out 1 and half turns and still have the same problem. As far as the ethanol eating the carb up theres about a 50 50 chance that was in there but I didn't see anything bad in the carb. nothing eating up anyway

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