I'm willing to bet this has been covered here somewhere and I've looked but can't get a good read on it. My boy's bike is an 05 YZ250F. After running terrible and figuring it down to a carb issue, we pulled it apart and did a thorough clean up. This seems to have been the culprit. Carb was filthy and after install the bike runs 100% better from idle to throttle response and smooth running. Problem is now when he let's off the throttle, the thing pops/backfires through the exhaust something terrible. I've also noticed that the header pipe gets VERY hot. after reading around here the general concensus is that this is pretty common. I just don't ever remembering it getting this hot(this was my bike from new until two seasons ago). Anyway, I have seen something about a possible mid pipe gasket leak causing this popping. Just wan't to get all the bases covered, from what i gather around here it seems an air problem is causing this? Any help? Thanks folks!