I would need to know what carb you are running. What is your ignition timing at idle at all in?.
i would check the reluctor in the distributor, I had a similar problem a few years ago on a older mp distributor, turns out the reluctor in the distributor looked like a mouse was chewing on it so where it passes the pick up it was not straight any more it was literally all chewed up. Once I replace the reluctor problem solved.
But your carb jetting/ adjusting and what timing you are at make a difference too if the reluctor is in good shape. Is the carb sitting on the intake or is there a spacer etc.
