Bac fire [rare] why

**murhf3** · 14th May 2005, 09:13

Had p.c.u added with new pipes,now and then and I must say not to often I get a bac fire on deacceleration, is it anything to worry about and what actually is a bac fire doing,i.e what causes it,to lean ,to rich ,timing?

**StoneChucker** · 14th May 2005, 09:22

If it's small "putt putt's" as you change down, I think thats relatively normal. Infact, I quite like the sound

If your exhaust falls off each time it fires, you might need to adjust something.

I don't know much on this, my thoughts only!
Back firing imho is when you have left over, unburnt fuel/air mixture in the chamber which ignites at a time other than when it is specifically supposed to do so. This happens when the exhaust gasses are not scavanged correctly, or quickly enough.

I'm sure if I'm wrong, some smarta, I mean, knowledgable person will correct me

As you can see, bad back firing would cause damage, as it would be pushing the pistons down when they are not designed to do so. Light "putt putt's" wouldn't worry me, as the pressure exerted would be minimal.

**dss3** · 14th May 2005, 09:49

Originally Posted by murhf3

Had p.c.u added with new pipes,now and then and I must say not to often I get a bac fire on deacceleration, is it anything to worry about and what actually is a bac fire doing,i.e what causes it,to lean ,to rich ,timing?

One reason for backfires is air leaks in the exhaust system, try checking area where headers bolt on and also where the can bolts on to to the exhaust, if applicable to your bike. Then again you may look after your bike better then me in which case you may not have these big leaks that I do. They make pretty flames at night anyway....

**crazylittleshit** · 14th May 2005, 10:01

what? what?

**zadok** · 14th May 2005, 10:06

When my bike did that my mechanic balanced/adjusted the carbies and it fixed the problem.

Marty

**Sensei** · 14th May 2005, 10:29

My GSXR does it but they all do . Looks excellent at night with a big Flame coming out of the Yoshy

**FlyingDutchMan** · 15th May 2005, 15:48

Mine used to till I changed to 91. Just means that sparkies aren't getting hot enough to self clean to unburnt fuel is going into the exhuast can catching fire there. 91 burns hotter than 96, so gets the sparkies hot enough to self clean and then you won't have any more back fires. Simple as.

**Hitcher** · 15th May 2005, 15:51

Mrs H's last Marauder used to do the most amazing backfires. Like a bloody great rifle going off. Only occassionally. When I least expected it. Shat myself everytime.

**Jackrat** · 15th May 2005, 20:09

On decellaration it's most likely to be an exhaust leak.
Seeing as how you just had your pipes changed it's the obvious cause.
Cold air gets sucked into the system meeting VERY hot gas.
This causes your back fire.
Get the bike hot,a short ride round the block,then retighten everything on the exhaust system.
Just give each nut a small tweek.
If your not happy with doing it yourself,just take it back to whom ever did the job in the first place.
This is as common as dirt with new systems, so don't sweat it.

**Matt Bleck** · 15th May 2005, 20:32

Yeah my bike does it too, dunno why, but it sounds good.

**murhf3** · 22nd May 2005, 11:13

Originally Posted by Jackrat

On decellaration it's most likely to be an exhaust leak.
Seeing as how you just had your pipes changed it's the obvious cause.
Cold air gets sucked into the system meeting VERY hot gas.
This causes your back fire.
Get the bike hot,a short ride round the block,then retighten everything on the exhaust system.
Just give each nut a small tweek.
If your not happy with doing it yourself,just take it back to whom ever did the job in the first place.
This is as common as dirt with new systems, so don't sweat it.

Thanks mate, sounds right, as pipes seem perfect colour, not to rich., and it seems to do it the hotter it gets. So as soon as the bloody rain goes away I will do that ,thanks.