Pull the air cleaner and look down the throat of the carb (with the engine off), and work the accelerator fully 2 or 3 times. You should see a good stream of gas shooting out of the discharge nozzles at the front. If not, it could be a bad accelerator pump, or a blocked passageway in the carb. Also, there should be a three hole positioning lever at the top of the accelerator pump, sometimes you can adjust the stumble out of it with that. It might be starving for gas. Check carefully for cracked vacuum lines. And with engine running, spray carb. cleaner around the base of carb, and all vacuum fittings- you will hear a change in rpm if there's a leak. Could be improperly adjusted floats, or a number of other things. Before you pull carb. though, thoroughly check your DISTRIBUTOR and ALL electrical components. (Points, HEI, etc...). If you have power brakes, make sure the booster isn't leaking. Post pics. if you can. Good luck.