my puch won't start. ive checked for everything i know of. great spark, clean carb with everything properly installed, exaust not clogged. i let it sit for about a month. then took it out on a ride for about 30 minutes, then it started to backfire and finally shut off. now it doesn't start up at all. is this is a jetting issue?? ive been running it on a 58 for months and it was running great, now all of a sudden this happens. anyone have any ideas?