I used to have a Quadrajet on my Camaro and it always backfired and popped when I used the engine to slow the car.
Then I put an Edelbrock on it and the backfiring was gone. But now its started to do it again. I just figured something on the carb needed to be tweaked a bit, so I fiddled around with the two mixture screws and it didn't seem to change anything. I really don't know what I'm doing when it comes to adjusting carbs but if anyone has suggestions of what to do that would be great.

 

Sometimes it's not the carb, but the timing. A new carb might make it go away because it runs richer and wont backfire as easily. Try putting a timing light on it and check the timing.

 

That's called "rapping", and if you have a free flowing exhaust, it's not all that uncommon. There is normally a small amount of unburned fuel in the exhaust (engines aren't 100% fuel efficient), and what you are hearing is the gas burning in the pipes. With a conventional, more restrictive muffler, you wouldn't hear it. Exhaust systems with catalytic converters burns the gas off inside the cat (that's part of it's job).

 

I reset the timing and it the rapping isn't as bad now, and the car runs quite a bit better. Thanks for the help.