Is your heat cross-over blocked? There is a port in the intake under the carb that allows exhaust to cross from one side to the other thereby heating the intake and carb base. There are certain weather conditions where this is a good idea, but it was designed in an era with entirely different gasoline. With today's highly volatile gas, it will boil the gas out of a carb. Blocking it is as simple as changing your valley pan. Something we have been doing since the 70s.

Notice that some pans have the smaller hole in the middle for the exhaust and some don't:

www.manciniracing.com/valleytrays1.html