Sounds like a vapor lock condition caused by "heat soaking" when the car is shut off. I suppose you could also have flooding caused by fuel percolating out of the float bowls, but you should be able to overcome that by cranking the engine with the accelerator pedal held all the way down to the floor.

Make sure the fuel line is not running too close to any hot surfaces such as the exhaust header or exhaust pipe. If you can't move it, you can shield it or insulate it to keep the temp down. Also make sure your fuel pump is strong.