backfire

The question i have is, the engine in my truck is a smallblock 400, bored 40 over, 11.5 to 1 comp, big cam, not sure of specs, single plane manifold, 850cfm edelbrock carb, after warming up the engine and goin to take off, it backfires up through the carb at times, i've been told it sounds like i need a little more advanced timing. the engine is a 1979 motor rated at about 475+ horsepower. any ideas?.also discovered tonight, that after driving for a bit, now it wants to diesel on me now.....lol, when it rains it pours....lol. thanks.
Brian