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Anthony Marceau

1986 Yamaha Moto4 200 YFM200 Ignition problems! Please help!!

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Hi everyone! I have a 1986 yamaha moto4 200 that's been sitting for a while! Cleaned the carb, replaced engine oil, put fresh gas in it. Got it running and went for a ride! It was running great just a little backfire once in a while! I barely made it home on the way back and now the bike won't run at all since then! It will start if I give a little bit of throttle but dies instantly as soon as I let go off the throttle! And even if I try to rev it up it'll sound like its not getting enough gas.. it revs up a couple hundred rpm's and backfires through the carb.. it almost sounds as if I was trying to take off from zero in 5th gear! Nothing is seized though! I dissasembled the head and the piston and cylinder are fine! Rebuilt the carb, replaced the ignition source coil.. I don't know what to do anymore.. compression test shows 90 psi Specs are 128 psi but i'm not sure if I trust my compression tester.. any ideas? Thanks!!

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Clean the  carb and  look  closely  at it for  plugged  holes  in the  sides of the jet  tubes . Blow  out the  passages  in the  carb too.  Your  description of the  problem  is classic lean  running from  fuel  starvation caused  by a plugged  jet or passage .

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Done, done and done! I just rebuilt the carb yesterday with brand new parts.. the carb is clean! I noticed it's spitting gas mist from the carburetor as if the intake valve wasn't closing all the way! Valve clearances seem good and timing too! 

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I agree with @davefrombc sounds like a lean issue. Check out this similar topic:

* Added full ATV info into topic title.

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Check any wires near your throttle. My polaris trailboss was acting similar and I have a short that acts up whenever I use the throttle.

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