On my way home yesterday my 1995 Chevy Blazer, 4.3L V6, backfired with black smoke coming out of the muffler, then it wouldn't start. When I got it home I changed the distributor cap and rotor. But that didn't work. It sounds like it's trying to turn over, but not getting there. Any ideas?

 

I'm starting to think it's a timing problem.. that means I have to time it while it doesn't run, anyone know how to do this?