Does anyone know what is the cause of back firing when de excelerating please ??

generally speaking its a lean out condition.

Usually either the tune or an exhaust leak. Newly fitted pipes? Check they're still tight at the heads.

Singular large pops out the exhaust on decel, particularly after the throttle is open wide and then snapped closed quicky, are often caused by a rich mix.
More often the multiple pops on moderate decel are caused by a lean mix.
Is your bike fuel injected? If so, whether it's too rich or too lean it can be tuned out by a competant tuner using the decel enleanment and/or a/f ratio tables.

Its a carby model and does it after heavy acceleration and then back off the throttle. I dont think there is any leaks at the head pipes, i started it when cold and put my hands around it and couldnt feel any air. Looks like i might have to play with the carby and lean it out a bit.

Actually...If its just started doing it - and this ASSUMES you have not done any mods recently; then it could be several things:
- The manifold intake seals could have gone west - fairly common and cheap/easy to replace
- The exhaust pipe seals have gone west - common as well and again an easy and cheap fix

The last thing I would be looking at would be the carby.

The bike has done it since i bought it a month or so ago. It has V & H slip on's on it and after having a really good look around the whole system there does seem to be a lot of soot where the slip on's join and also where the balance pipe connects, would this be the problem if its leaking ??

soot around those areas is a good sign its leaking

you will need new gaskets for the balance pipe & probably best to get new clamps as well.

Cheers for the comments, I will start with the exhaust pipe joins and see what that does.
Thanks again.
BJ.

OK, I have re- sealed all the joints on the pipes and can not feel any leaks, but still have the back firing or popping. It was pretty cool to listen to it back firing and popping but now its just annoying.
Any more ideas ??
BJ

tussuck 

Actually...If its just started doing it - and this ASSUMES you have not done any mods recently; then it could be several things: 
- The manifold intake seals could have gone west - fairly common and cheap/easy to replace 
- The exhaust pipe seals have gone west - common as well and again an easy and cheap fix 

The last thing I would be looking at would be the carby.

 

 

tussuck,  The manifold intake seals, are they the ones that join the air intake from the carby to the heads ??

BJ.

 

 

It's a lean condition. You will need to adjust the carbs.

We had similar issues when we re-jetted the Yamaha cruisers we use to ride, and is generally associated with it running too lean. One way to see if that is in fact the issue is pull the choke out a little. This will richen up the circuit - If the problem goes away - Then you know what the issue is.

Good suggestion mongrel. Umm err whats a choke?

Cheers guys, i will try the choke out a bit first and go from there.
BJ

Any update on this mate?

I have put the baffles back in and this has toned down the loud back fires and leaving the enricher out does seem to make a difference, so when i feel a little better i will give the fuel a little turn. Thanks for all the great info guys.