GM-GMC: 1983 K35 4WD, intake manifold gasket, power brake booster

Question
I have A problem with missfiring and backfiring through the carb. I know you only deal with diesel engines but might have some idea. Engine is a 350 with 4 barrel carb, just started while driving. Replaced cap rotor plugs and wires still does it. Checed timing and ok, any Ideas
Thanks Jesse

Answer
Lots of possibilities, but most involve vacuum.

The carburetor could have a vacuum leak.  The intake hoses (from devices such as vacuum advance, power brake booster, transmission modulator, etc.) could be split and leaking.  The intake manifold gasket could be leaking.  You could also have a sticky valve.

Get a vacuum gauge, connect it to the intake manifold, and see what the reading is.  Unless you live at high altitude, the reading should be steady and around 18 inches of vacuum.