Backfiring while driving

[1972GMCsierra4x4]

So my old truck likes to backfire once in a while while I'm driving it. I rebuilt my carb a couple of weeks ago, and when the choke is set to the factory spot, the truck will occasionally backfire when I'm accelerating. The carb is an 600cfm edelbrock 1406 with electronic choke. My engine is a 350 with 62cc heads and a compression ratio of about 10:1 (if my math is right.) If I set my choke to very rich the problem is solved and my truck runs great. I need to know though if this could be a more serious problem or if I'm just running the wrong size of carburetor.