I just purchased a worn out 450 about a month ago. The bike started cutting out when it got hot as I would hit the gas. It would idle fine. Had the top and bottom rebuilt by reputable company. Motor was shredded. Put motor back in bike and broke it in according to recommendations. Ran fine. Took bike to the mountains to ride and after about a hour the bike started doing the same thing,ie(cutting out on acceleration, backfiring, stalling,etc...) Still idles along fine. I'm at a loss.. Any suggestions would be greatly appreciated