Motorcycle Repair: Backfiring, air fuel mixture, piston stroke

Question
Chris, I just finished rebuilding my carburetors on my Rebel 450. I have the problem of backfiring when I hit the kill switch. I have tried to adjust the pilot screw to get the right mixture, but when i feel it is right, the backfiring occurs. I can get it to not back fire, but that is when the engine is not idling on its own, but with me manually controlling it. Is this just an air/ fuel mixture problem, or what? I have all carb settings at the manufacturers stock specifications. What is going wrong?

Answer
Hi Adam.
 Backfiring is not a product of mixture.  It occurs when the exhaust valve is opened up during the firing phase of the piston stroke.  This fries valves and costs power.

Check your valve gap and ignition timing.  Fix that and synchronize your carbs.  That should eliminate your backfiring problem.

Let me know how it goes.
Good luck.
FALCON