I'd question the float level, and maybe also the need for an insulating spacer (phenolic) beneath the carb to keep it from soaking heat from the intake. If your float level is too high the residual heat in the engine can heat up the fuel in the bowl, expand it and cause it to dribble into the intake giving you a flooded condition. If you let it sit long enough to cool down that fuel has time to evaporate, and it starts better. Another thought, you've not mentioned what type of fuel pump you're running, but if you're running an electric pump without a regulator you might be on the ragged edge of too much pressure, and when you shut down the fuel line pressure goes up with residual heat, pushing past the needle & seat, flooding your bowls and overflowing into the bores. Just a couple of options to consider.