qfo

So i was wondering how bad are backfires for the engine? Are the pulses produced from the explosion outside the combustion chamber powerful enough to disturb the exhaust gases and burn an exhaust valve? Im asking this because i was making my bike backfire the other day by playing with the kill switch so i'd like to have your opinion on it. Thanks

mboe794

I believe the proper term would be after-fire, or after-burn. They do happen on occasion and it's usually not a big deal. Mine does it sometimes during startup if it doesn't fire up right away. However, I would not recommend intentionally generating an after-fire. This phenomenon is obviously not a part of the normal operating conditions and IMO should be avoided if at all possible. I would think the pressures could possibly damage the header or other parts of the exhaust system.

GTS

In general they aren't going to hurt anything if they happen say on decel due to a lean or rich condition. But those are generaly relatively small. However when you cut the ign. off there is way more fuel going into the exhaust and when you turn it back on and it lights off it has a lot more power. You could potentially blow out a muffler or exhaust pipe, though those parts on these bikes are pretty well built. You wouldn't ever burn a valve per se however if it was bad enough it could potentially blow the exhaust valves open and if your timing was just right you could potentially have the valve hit the piston. This would be a very extreme case and highly unlikely.

So I guess the short answer is no it generally won't hurt the bike, however if you do it big enough there is the potential to cause some dammage.

speedkelly@aol.com