Backfire! What is it exactly?

**mattian** · 5th September 2011, 16:34

Not sure if I am posting this in the right place. My knowledge of engineering is limited and thought this a great place to pick your brains Kbers.
I've got a 2009 Suzuki SFV 650 Gladius. Done close to 50,000 ks now since I bought it at the start of 2010.
I just love that V-twin rumble and the way it growls... love nothing more than giving it a little vroom vroom when idling at the lights. Was doing it the other day and on about the 3rd "vroom" it backfired... was kind of like a loud bang/popping sound. It's never done that before and as my knowledge of the inner workings of engines is quite limited instantly thought of the the worst case scenario.
My question is. What is a backfire exactly? is it a symptom of something that might be wrong? something I should be concerned about?
thanks all in advance.

**blackdog** · 5th September 2011, 16:53

Unburnt fuel igniting in the exhaust system. Tune up time for plugs, airfilter, valve clearances.

**slofox** · 5th September 2011, 16:56

"What is a backfire exactly?"

As far as I know...Unburnt mixture in the exhaust system igniting.

We used to deliberately induce backfire in cars by turning off the ignition, coasting along, in gear with throttle held wide open. Then turn ignition back on. Boom. Sometimes anyway...

**mattian** · 5th September 2011, 17:01

thanks fellas. Mite try that one Slofox... sounds like it might a new strategy to deal with tail-gators..... flame on

**bogan** · 5th September 2011, 17:07

Had a guddun in my shed when I was cranking the bros over (cranking=less voltage to the coils and weak spark), bloody loud in enclosed spaces, just about shat meself!

**blackdog** · 5th September 2011, 17:07

Originally Posted by mattian

thanks fellas. Mite try that one Slofox... sounds like it might a new strategy to deal with tail-gators..... flame on

It won't work in a modern EFI car. Carbs only.

**imdying** · 7th September 2011, 11:51

Originally Posted by blackdog

Unburnt fuel igniting in the exhaust system.

That's an after fire, back fire is back through the inlet tract.

**BoristheBiter** · 7th September 2011, 12:27

Originally Posted by slofox

"What is a backfire exactly?"

As far as I know...Unburnt mixture in the exhaust system igniting.

We used to deliberately induce backfire in cars by turning off the ignition, coasting along, in gear with throttle held wide open. Then turn ignition back on. Boom. Sometimes anyway...

arh yes fun times, bring back carbs, just to see the people in bus tops jump.

**bogan** · 7th September 2011, 13:22

Originally Posted by imdying

That's an after fire, back fire is back through the inlet tract.

Can lead to a normal fire if you run over-oiled pod filters too

**imdying** · 7th September 2011, 16:08

Yikes.... or singed eye brows if you're playing with a rooted Holley

**5150** · 8th September 2011, 14:07

My bike is fuel injected, and it also has aftermarket exhaust system. It backfires and pops like crazy when I back off. I kind of like it. I have been told that sometimes if there is a gap in the system (air leak) and when you back off the throttle, all the unburn gasses try and go back through the system, the air from the air leak mixes and it ignites causing the back fire. Been told to tighten all the manifold bolts, and check for loose fittings in the exhaust system. The other thing is that if you are running an aftermarket system and haven't chipped the computer to suit the new system it can run quiet rich being prone to more backfires. Just my 2 cents worth

**DEATH_INC.** · 8th September 2011, 14:53

Originally Posted by 5150

My bike is fuel injected, and it also has aftermarket exhaust system. It backfires and pops like crazy when I back off. I kind of like it. I have been told that sometimes if there is a gap in the system (air leak) and when you back off the throttle, all the unburn gasses try and go back through the system, the air from the air leak mixes and it ignites causing the back fire. Been told to tighten all the manifold bolts, and check for loose fittings in the exhaust system. The other thing is that if you are running an aftermarket system and haven't chipped the computer to suit the new system it can run quiet rich being prone to more backfires. Just my 2 cents worth

Nope, modern bikes have 'air injection' into the exhaust to burn the extra gas in there and trick the greenies into thinking they're carbon friendly. That's what 'block off plates' get rid of.

**DEATH_INC.** · 8th September 2011, 14:55

Originally Posted by imdying

Yikes.... or singed eye brows if you're playing with a rooted Holley

Ever seen what a Predator on a warm 351 V8 does? It's like a nuclear mushroom about 10 feet high....

**5150** · 8th September 2011, 15:14

Originally Posted by DEATH_INC.

Nope, modern bikes have 'air injection' into the exhaust to burn the extra gas in there and trick the greenies into thinking they're carbon friendly. That's what 'block off plates' get rid of.

Would that be in the exhaust system itself? (Cat converter and such). If so, What happens if you gut the original system and replace it with an aftermarket race/sports system then?