I bet the fuel is hitting the engine AFTER the tank is full. The pump pumps the fuel in, and when the tank is full the fuel needs to push up and oout of the vent, but is also pushing out of the carb line. You don't know the tank is full until the fuel squirts out of the vent line, but by that time the fuel has been presurizing a full tank for maybe a full second. I'm not really familiar with your engine, but if you close the needle valve(s) before fueling, that might stop the flow while filling up. Another thing that may help (enough) is to put the prop in a position where both intake valves are closed. That will at least keep a ton of fuel out of the engine,and the fuel in the intake tube can just be the prime for the restart. Might work, no?