Right I got a kxf250 2004 had a new topend with new stage 2 hot cams. Been running great apart front the jetting but I got that sorted. I took it to a track once I come home I jet washed it Dried it put it away, cleaned the carb changed spark plug and it wouldn't start just backfired. We now have really cold weather and bikes in the garage so it's freezing its been about 1 week since its last started just backfires, iv been told it could be the valves it hasn't got a lot of compression so in starting to think it need valve clearance checking, but what's confused me is its only been 1hour since the rebuild so could it be the vales ?? please help! I can't think what it is!