Remove the air cleaner and watch down the carb for a squirt of fuel while you open the throttle. Sounds like a bad accelerator pump. No cost to try and easy to do. If not that bad power valve or its equivalent if not a Holley. Smooth running if you baby it is a clue.
Ron


In sixty-five I was seventeen and running up one-o-one I don't know where I'm running now, I'm just running on Jackson Browne-Running On Empty