@adam posted:Sounds like you could be boiling the fuel in the carb. When that happens you will get a very slow/hard crank or a almost no crank. Easy to see go out for a drive and when you get back use a infra red temp gun and see what the temp is top of the intake compared to the carb base and bowls.
If this is happening to you then adding an insulated gasket might fix it. Here is one by Edelbrock.