Trade Street Demon 750 carb for 625 carb or other

I think I purchased too big of a carb for my car. Carb is a 1904 Street Demon. I have been combatting an off idle stumble and have tried several squirter sizes to compensate. Called Holley and they say the carb may be too big for a stock 340. Anyone buy a 625 Street Demon they feel is too small for their application? I live in the Northeast and would be willing to trade as long as your carb is in new condition like mine is. Thanks