Trouble Reving

[jonathan180iq]

Well, exhaust systems aren't closed systems. There is always ambient flowing around air inside the muffler. For example, if you look at the bottom of the muffler, you can see little holes which allow trapped moisture to escape and which also let outside air in.

As far as what you were describing, slight popping and gurgling sounds aren't considered afterfire. And I have experienced then also when in a lean mixture.
Afterfire is the serious bang that everyone has heard at some point in their lives, but it comes out of the exhaust.

Like I said, it is mistakenly referred to as backfire.

I'm not a chemist or physics expert, so it's possible that afterfiring can occur in a lean mixture, I just don't see how it could happen. When there is too much air in cylinder, an engine doesn't experience a proper explosion. It would make sense to me that a lean mixture which carries over into a muffler would then encounter even more air, which would essentially kill the flame.

I may be wrong, but I'm pretty sure that's how it works.