I too experience this problem. We also have the mandatory 10% ethanol blends and have come to the conclusion that a a vapor separator is probably needed.

It sucks though. Go for a cruise. Car starts and runs just fine. park for a half hour and she won't start. Pedal to floor crank and eventually she'll fire. Very frustrating.

I got a separator from the last swap/show. Now I just need to cut my nice new steel braided carb supply line... and install a return line.