[typesix]

If it's vacuum leak, fix that first. Gaskets at carb may be dried up and allowing leak. I had such a problem with my former 74 Dart 318. Rebuilt carb and same problem, installed rebuilt carb and still had vacuum leak. Ended up sealing the horizontal gaskets on the rebuilt carb with gasket sealer where visible on exterior of carb and this fixed the vacuum leak. Spray carb cleaner around the carb gaskets (carefully, it's flammable) to see if leak is there, check hose connections.