What causes backfire?

**TYPE-R617** · 10-01-2008 10:09 AM

As above, never had back fire before until i got my full exhaust changed. I get back fire in when i change to second and third gear. Can anyone tell me what causes this? Thanks in advance.

**SPEEDCORE** · 10-01-2008 10:14 AM

I don't think you are actually experiencing backfires, if you just got your exhaust changed. What you are experiencing is most likely just the popping and crackling that you get with larger diameter pipes and less muffling.

**TYPE-R617** · 10-01-2008 10:40 AM

well i've had my exhaust changed for over 3 months or so now. yeh it's a popping noise, but only pops once but not really ear blasting sound but just enough to hear it. it usually happens when changing from 1st to 2nd and 2nd to 3rd.

**BlitZ** · 10-01-2008 10:44 AM

backfire it caused by unburnt fuel... ie, when fuel esacpe the cyclinder and goes into the exhaust they get ignited.. than.. kabooooooooooooooooommm!!!!

**TYPE-R617** · 10-01-2008 10:47 AM

can it also be caused by old spark plugs in anyway? (sorry for being a noob)

**minix33** · 10-01-2008 10:51 AM

when you change gears and for a moment you are not accelerating, the engine runs without enough oxygen in which case the unburnt fuel goes into the exhaust pipe which is the ignited when the engine does fire.

**minix33** · 10-01-2008 10:54 AM

Originally Posted by TYPE-R617

can it also be caused by old spark plugs in anyway? (sorry for being a noob)

considering the spark plugs are responsible for igniting the fuel, old spark plugs may be inefficient causing more fuel to be unburnt and therefore lead to more backfire.