Question about my idle

When it's just idling around 1000 rpms my exhaust pops a hell of a lot. I don't have a resonator but a few people have told me my timing is off?? And there is like black stuff around the end of my muffler, and i've been told that i'm running rich, any of this true???? Thanks!

poping? Hmm. Well it's probably not this, but can't hurt to try.

Take a piece of paper and put it up to your exhaust, if it sucks it in, then you may have a bad vavle.