Odd engine behavior after first shutdown of the day

[jhv48]

I also live in California and every carbureted engine I’ve had in my cobras over the last ten years have exhibited similar symptoms.
And I came to the conclusion that it was the low boiling point of our blended crappy California gas. Without a return line to the fuel tank, after shutdown, all that fuel in the pump and lines wants to boil and vaporize.
Tried spacers and different carbs. No change. Just learned to live with it.
After hot restart, it takes a minute or two to flush out the hot fuel with fresh cool fuel from the tank then all is well.
Winter California gas formulas have a higher RVP index which means it evaporates at a lower temperature than our summer gas formula. So, the problem is worse in the winter. Supposed to help with air pollution. Summer gas formulas have a lower RVP index which raises the boiling temp slightly.
And, yes, EFI should solve the problem.