Driving highway 550 last summer ~90 degree day I couldn't run her wide open without repeated engine dying/surging... an anxious hour later I stopped at a gas station and saw little gas bubbles simmering in the filter bowl by the carb... I imagine it was worse in the carb. Driving up hills was really bad... limping along the interstate shoulder at 30mph playing with the choke to keep her from dying.
Once I got to the mountains and drove up into cooler air ~70degrees the problem disappeared.
That was with the stock fuel system on my 59 burb.
I'm adding a return line to see if it helps.
