How to keep fuel up to the curb after shut off.

Once in the carb's fuel bowl the fuel isn't able to get back to the fuel tank. Not possible in normal operating conditions. If the fuel in the line before the pump is returning to the tank you have tank venting problem. If it is after the pump you have a venting problem and bad check valve(s) in the pump.

This stuff that they call "fuel" these days is nothing like the gasoline of 20 years ago, and probably not even like that of 5 years ago. It supposedly meets the same Vapor Pressure spec as the fuels of old, but my experience with it begs to differ. I really don't think the corn lobby has done anyone any favors except for themselves.