I've had an open element for about a year now, and it was getting a bit dirty so I went out and bought a K&N filter. Now when I push it hard, the car backfires around 3000RPM. I was thinking I might tweak the timing but I don't know if there is another source of the problem. Thanks.

 

Check timing and plug wires - I have a plug wire that likes to come off, and when it does, I get a backfire.

 

Yea, it was definitely the timing. I advanced it about 2-3* and there is no more backfire. And while I was at it I replaced the distributor cap, and rotor. (They looked like hell, all pitted and corroded). Now it runs like a champ, thanks fellas.