Thanks Al. I think its a carburetor problem. I hooked up a vacuum gauge to the manifold and it jumps around a lot. It wont settle. Vacuum is working to the vacuum advance, vacuum advance works, timing is set.
When I spayed carb cleaner in the carb it seems to stop the backfiring when I revved it up. This is why I suspect the carb.
Do you know how I set the fuel mixture screws? I know on other cars it was turn all the way in then back it out 2.5 turns. Is there a formula for a 1968 Pontiac 350 with a 2 barrel carb?
