That can maybe be fixed by trying a different metering rod. Try finding Doug Roe's Rochester book. It really gets deep into the theory and what practical modifications really work. All the other Q-jet books are fine, but I found them more performance orientated. Roe's book concentrates more on stock carbs and their problems. Jet changes affect the entire rpm band. But metering rod changes affect idle, off idle, and part throttle. I have taken rods and jets from dozens of carbs and I can tell just by eyeballing them what to expect when I use one. Roe's book breaks them down by part number and gives specs about each one. So if you have a metering rod that is a little too fat [lean] where off idle or mid-range occurs, changing to a rod that is thinner [richer] at that point will solve the problem. The other thing to be aware of is that plenty can happen to a carb after 55 years or so. Many changes may have occurred. The Pontiac carb pages can be found at this site: Carb pages Look up your carb number and see what rods and jets were installed for the application. That is why I always say the carb that came on the car is the absolute best one and should never be changed. Here is an example of what info is on those carb pages. You should have # 45 rods and # 72 jets. EDIT: Don't drill jets!