Hi. After installing new piston, boring the cylinder and reinserting the camshafts the engine seems to bacfire or something??. i start the engine, it sounds good for 10-15 seconds at idle speed, then it "pops", and dies. the sound is comming somewhere from the air filter region, and i can feel the "pop" if i put my hand on the air cleaner joint. it does this everytime. the larger the RPM, the louder the "pop". i have not messed with the jets, other than the idle speed screw. im not sure if this is your ordinaty backfire, my experience of backfireing is that you hear a larger explotion from the exhaustpipe and the engine keep running. now for me, the sound is not so large and doesnt come from the exhasutpipe but from the aircleaner joint as i said, plus the engine always dies. im not 100% that my camshafts is correct aligned, as i have installing them myself and im novice. they could be off 1 pin. read more about my camshaft installation (and why it could be wrong) here: http://www.thumpertalk.com/forum/showflat.php?Cat=0&Number=964969&page=0&view=collapsed&sb=5&o=all&fpart=&vc=1 could this be the problem?