REPOST Enforcement Mod
Join Date: Feb 2006
Location: Wesley Chapel, FL (The Dub-C)
I've merged the threads. There's no reason for the second one.
How would backfiring into the airbox cause the crankcase to over pressurize? A "back-fire" is usually a constant flame propagation out of the combustion chamber back up through the carbs (throttlebodies for fuel-injected systems, but it's very rare for that to happen). It's usually not a "pop" as much as it is a quick burning flame.
From what you're describing, the flame propagated out of the combustion chamber, up through the throttlebodies, and instead of the pressure escaping out the massive ram air duct at the front of the bike, it went back down through the 3/4" crank breather line, pressurized the crankcase, and then back up through the cam chain tunnel to pop the valve cover gasket. Is that what I'm reading you think happened? Sounds really far-fetched. Not saying it couldn't happen that way, but it's not plausible. I'd expect you to blow the airbox apart first or the pressure to go out the front of the bike before it had any chance of overpressurizing the crankcase and popping a valve cover gasket.
So, do you have a leaking injector? One that allows fuel to go to one cylinder while it's sitting for awhile? And then on startup, it ignites the raw fuel and the flame goes back up the intake track? The valves should be closed in this instance so I'd be inspecting the fuel injectors and the valves not sealing properly as the first thing. It may also be a bad or intermittent crank sensor or camshaft sensor as well as already stated.
I may not be perfect, but at least I don't ride a Suzuki.
Ridding the Internet of bad grammar, 1 post at a time.