<VV>Vapor Lock

[Padgett]

One other remote possibility is a crack in the suction line that is closed 
when cold but opens when heat expands it. In that case it will pull in air. 
Might check for a dark area when hot but before cranking.

Keep in mind when the fuel level is high (level in tank is above the fuel 
pump) you will get a gravity feed but not with a minimal fuel level.

Which reminds me, don't Corvairs have vented caps ? Blocked vents can do 
all sorts of things.

Padgett