Sounds very much like the carb is getting hot and boiling over. A good 4 hole phenolic spacer should improve performance and solve your problem if you have room for one. Depending on which Carter pump you have you may need a regulator and or a vapor return line. A hot carb with residual line pressure of more that 6.5 psi is asking for what you are experiencing. What is your fuel pressure running and at shut down?
