Quote Originally Posted by wbute View Post
With a stuck valve you have no fuel going in or out of the cylinder. It can't backfire. Backfiring through the exhaust is unburnt fuel igniting in the exhaust system. Through the carby is timing. It will miss with a stuck or burnt out valve.
Not if it's the exhaust valve that's stuck open. In that case a lot of fuel will go straight out the open exhaust valve into a hot pipe and burn in the exhaust system before the spark plug can fire it.