Could be your fuel check valve is allowing all the fuel to run back to the tank and siphoning out your fuel bowl. Even though you have decent performance when it is running, it could be a fuel pump issue. If it is time for a fuel pump and you do not run this vehicle often, you might consider installing an inline electric fuel pump.. It's AWEsome for my vehicles that sit a long time between starts... just turn the key and let it pump fuel up to the carb and hit the key.. starts every time!
the following was designed for EFI vehicles, but has fittings to work for carb'd vehicles as well... basically an inline check valve that keeps your fuel from draining out of the fuel lines. Works really great if you have a bad check valve or do not want to replace fuel pump
http://www.surrauto.com/documents/CKV5CKV7.pdfBefore you try to start when it will normally fail, take off your air cleaner and see if you are getting fuel... if the vehicle is REALLY hot, might be better to use a mirror to look into the carb and see if you have any fuel squirting into the intake. If there is NO fuel coming out, or very little, the above condition may exist. It could also indicate the fuel boiling out as MrFast posted. Do you have a phenolic spacer under the carb?
If this engine has headers it can dramatically increase the under hood temps. If it is lacking a phenolic spacer, that would make things worse. If the fuel lines running near the exhaust are unprotected, that can also contribute as it heats the fuel.
