My 80 will dribble fuel out of the carbs if its tilted fully up for towing.
I wonder if you left your fuel tank vent shut and the fuel hose connected?
Trimmed up the carbs may dribble out of the float chambers through the main jet because of the extreme angle, and the fuel was being replenished by the pressure in the tank caused by warmth and slopping fuel?
I always run mine out of fuel by disconnecting the hose and leave it disconnected before towing.
I am usually not as green as i am cabbage looking.