De-acceleration popping sound/back firing...

[Giorgio68]

Does anyone have any idea why I am still getting back firing on de-acceleration on my berlina 2000.
I have replaced the carbs with new Webers 40DCOE sidedraft, new pointer, new plugs, wires, distributor cap, reset timing, almost anything you can think of. The only different thing I have in the car is straight pipe on the back.

[Tifosi]

When in doubt and you're positive it's not coming from anywhere else, look for leaks in the exhaust, (got black soot? then you got leak), right from the manifold gaskets to every joint, seam and weld on the whole system.

It doesn't even have to be a leak big enough to hear, but just enough to let a blast of fresh cold air into the system during deceleration (particularly while 'engine braking') and from that moment on, it's plops, snorts and crackles out the tailpipe.

[BlpltGTV]

I think its what really free flowing exhausts do. Or you might be jetted just a little bit off. Both of my cars crackle off throttle, the Alfa not as much, but the Datsun sounds every bit like a race car, and from time to time will emit either a nice blue flame kernel, or from time to time a large orange fireball from the tail pipe. If you have a slip fit exhaust, you will have small leaks, with a fully welded exhaust, its still easy to get a leak. Since you have carbs, the weather will also affect the mixture as well, so it might go a little rich, or lean depending on the day.
If it were me, I wouldn't worry about it.

Will

[lazydays]

I just replaced my exhaust with an alfaholics sports exhaust and found it had a small crack in the exhaust manifold - the popping has reduced significantly now so i think this thread is spot on

[Alfacliff]

turn the idle air adjust screws out 1/4 turn at a time till the popping stops. works on my 74 with delortos, works on my 80 yamaha, works on my 2006 triumph bonnieville.
cliff

[lowmileage]

Quote:

Originally Posted by Giorgio68 Does anyone have any idea why I am still getting back firing on de-acceleration on my berlina 2000. I have replaced the carbs with new Webers 40DCOE sidedraft, new pointer, new plugs, wires, distributor cap, reset timing, almost anything you can think of. The only different thing I have in the car is straight pipe on the back.

[jarrington]

I've got the same thing on my Spider, which has Sprint Filter sport air cleaners and a stinger tail pipe.

I kind of like it.

Cliff, are you suggesting a too lean mixture?

-Jason

[Chsmadden]

I've always wanted it but could never figure out how to make it happen.

If it's a steady pop-pop-pop. That's most likely normal.
If it's a single BANG, then you're probably a little on the rich side.

[jarrington]

Mine's a steady pop-pop-pop when off-throttle. Seems to be a bit louder since I set the idle mixture with a Colortune.

-Jason

[Alfacliff]

I dont know if its rich or lean, I only know it works. and has for every carburetted engine I 've had.
cliff

[La Voce]

popping during deceleration means you have set your idle mixture too lean. back out your idle screw 1/4 turn on each carb and go test drive until the popping stops.

[La Voce]

For clarification, I meant idle mixture screw, there's four, one for each carb throat. Did it work? Are you good?

[Giorgio68]

Quote:

Originally Posted by La Voce For clarification, I meant idle mixture screw, there's four, one for each carb throat. Did it work? Are you good?

[jarrington]

Quote:

Originally Posted by La Voce For clarification, I meant idle mixture screw, there's four, one for each carb throat. Did it work? Are you good?