Just with the limited info ... sounds like a vacuum leak. Just a shot in the dark, but look over all the lines and while its running with the choke check with carb sray around the base and see if there is a leak there. Never hurts to clean the carb with good old carb cleaner. Not much to those old carter 2bbl, but when they operate wrong they can be annoying. Good luck and let us know how its going.