I have heard that you can make a carb spacer out of a hard wood to insulate the carb from the hot intake manifold. I would try a half inch spacer and see what happens. If you are afraid the wood could be a fire hazard (about a thousand to one shot I think) you might try some sheet pcv cut to size. You also might try opening the hood after you stop, to let the heat escape faster. And last I have heard the ethanol mix gas (which runs perfect in my '49 6400) has a slightly lower boiling point.