vapor lock...
driving it is warming up everything under the hood, gas vapor's easily with heat, when it restarts, then it's using the last of the built up fuel and pressure from the expanding gases, then the vapors hit's...it's like sucking a coke with a straw with a tiny hole in it....and then you hit the gas pedal and your actuating the accelerator pump in the carb...and that's just feeding it just enough fuel to stay running. but not running to peak performance. Air flow, insulation, and a better fuel pump with a fuel pressure regulator, should help.
Carbs are a bitch. Elevation and temperature sensitive to the tips of your teeth.
now if you live in Minot, North Dakota, or Alaska..... and your having these problems.... that's a completely different story.