I know that a 302 is one of the simplest engines ever built and probably one of the best, but I am having trouble tuning mine. Its a 68 motor sitting in an 85 Bronco. Has 2v carb on it still and I just rebuilt it because A: it was an original carb B: it was filthy and ran a little rugged. After jetting it down and new gaskets i put it back on and started in on the mixture. Thought I had mixtures right so I went to work this morning and noticed that at low RPM's cruising through town it seemed like it was loading up, then on my way home it was back firing. Timing issue on that I thought so I adjusted the timing and while I was at it I messed with the fuel/air ratio. Timing did nothing for the back firing but the carb loading seems to be a little better after adjustment. Any ideas?

 

You may have the air/fuel mixture a little rich yet or your choke may not be opening properly.