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I have a 2005 crf 70 with a big bore kit from tbolt usa and now its an 88cc. The kit came with everything including an air filter carburetor and extra jets and a race head that I installed the valves. I dont hear any valves knocking and i followed the instructions and installed them with a .002 gap so i dont think they are to tight.  


When in neutral if I hold the throttle wide open it spurts and then backfires and i can tell it wont rev to its limit. when in gear it rides nice until i hold it from about 50%-100% throttle then i can feel a lack of power and it bogs.

It has a #88 main jet and i went down to a#85 jet then #82 jet and up to a #92 jet cause i wasn't sure which way to go either bigger or smaller. The #92 jet felt the smoothest but it backfired once while riding so i thought it was to big a jet. If not i still have a #95 jet i believe. I messed with the air screw and its at the highest rpm. I havent touched the jet needle yet I'm not sure if I should.


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