YDIS backire
 

I'm running an xt 600 motor in a Wasp sidecar motocross outfit. My problem is that i have a backfire through the left hand carb on tickover, i've done all the airleak thing and put on new inlet manifolds, the carbs have been sonic cleaned and the little diahragm in the side replaced.Sometimes it backfires and stops the engine dead....Any ideas????

Bad ignition timing.
Bad valve timing.
Untight inlet valve.