Backfire on deceleration

[erik_w]

Hello!

I've got a four stroke, two cylinder, two carb (no balance) bike and I am having problems with backfire on deceleration. It happens after running hard in top gear and then quickly slowing down, such as getting off the freeway. When I let off the throttle and put in a lower gear the Engine backfires throught the exhaust.

My theories are either:
- The pilot Circuit is either too rich or lean
- The ide setting of one of the throttles is too low

What do you Think?

Erik

[Vasco DG]

Exhaust air leak.

[Chuck in Indiana]

Exhaust air leak.

More than likely. Idle jet could be a little too small. Personally, it doesn't bother me. Fighter planes (and Mouser) do it..

[redrider]

I vote for exhaust leak. Way back in the dark ages, those non riders in the know told us it was an ignition problem. Later, during the age of enlightenment, Kawasaki gave us the clean air system of injecting fresh air into the exhaust to fight emissions. I always had a pop pop on throttle shutdown on the GPz 550. The GPz 1100 did it with a pipe and filter change on decal. Kind of a nice crackly burble thing. Hot weather means less O2 per chunk of air (density) so you may be a bit rich and the air leak completes the combustion process in the pipe.

[Groover]

I had this issue, and although 50% of the times I loved the popping, I just wanted to clean it up so-to-speak. All I did was open (turn counter clockwise) the low end needle circuit 3/4 of a turn on each carb (30mm Dellortos) and the popping is gone. I'm much happier now having the Guzzi vacuum-sounding-roar when closing the throttle on decelleratiom (e.g approaching an exit ramp) over the race-ey popping.

There are other reasons for the popping as suggested and you'll find over the web, but in my case it was just a lean low end circuit that luckily I was able to adjust without changing the jetting, so I'd suggest trying that.