BIS backfire

[Gadge]

Does anyone know what the causes of a traditional car backfiring sound can be? Mine is doing it terribly when you come off the throttle after you've done a short stint at around 50-60 mph? It's a proper "pop" like a firecracker. The engine runs sweet and is not missing a beat so I'm thinking it's the fuelling?

Any ideas?

[126_bis]

Mine done that when I picked it up but only after pushing the throttle all the way to the floor and then releasing it.  If you look through the top of the carb if you lightly push the throttle only one butterfly opens when completely depressed it opens both I wonder if it is over fueling.  Like you said back in my post I've got the electric fuel pump so might just be a slight over fuel. 

[Gadge]

Hmmm Might run it on my gas analyser and see how rich it is. I'm thinking that as I let off the throttle the idle mix may be set too high thus over fuelling it hence why it only does it after throttling   

[gammakeith]

Backfiring can be due to an air leak at the manifold which is why cars with broken exhausts often do it.  For reasons I have never understood, motorbikes tend to do it if they are running lean.  I would have thought it should be the other way around as there would be more unburnt fuel but that has never been the case in my experience.

Keith

[Gadge]

Thanks Keith ironically I've just sorted the blowing exhaust I had by filing the mating surface at the exhaust end and fitting new gaskets and it sorted it out however I never noticed it before when it was blowing. I get a strong smell of fumes when it's ticking over so I'm wondering if it's too rich