Motorcycle Repair: yz80 misfire, yamaha yz80, intake leak

Question
I have a 2000 yamaha yz80 that backfires before the powerband.I have tried to rejet it and clean the carb,but it just won't run right.Do you have any idea of what it could be?

Answer
Matt, while the bike is running at idle, try spraying some carb cleaner to the carb boot where it attatches to the engine, If the idle goes up or the bike dies, you have an intake leak. Also look into the baffle inside the muffler. Sometimes they come loosened up and bunch up causing a very similar issue..

Hope this helps!

~Mark