Fuel Evaporation

Likely a combination of evap, fuel boil, and vapor lock. "This new ****" they are calling "gasoline" has a fair amount of alky in, and it boils very easily, and has a much higher vapor pressure than straight gasoline

Before I converted mine to EFI, and later tore it apart, I went to a rear electric pump, added a carb heat isolator, and made a fuel return system much like my 440-6 or the hemi's used, and later jeeps. You can buy a couple of Wix fuel filters that already have the return orifice built in. I used to know the part no.
EDIT I ain't fully senile yet!! Wix 33040, 33041