It would be as well to let everyone here know what fuel system your car is running. I'm assuming by the age of the car, its not a fuel injection engine, but as its in the USA, I'm not completely sure? If its a carb engine, I think there are three carbs which micht be fitted, an SU, the Solex/Zenith, and a Pieberg. Sounds like it could be running rich at 'warm' start,and there are different ways the cold start devices work, so we need to know what the fuel system is. I'm sure there will be someone on the forum who can help, once we have the information