Hello!
Don't use any fueladapters like Robarts and similar items..there is much better, more easy way to fix it.
Here is what you should do
You use an ordinary fueltank but instead of using 2 fuellines you use 3 : one goes to the throttle (as usual) one goes to the silencer (pressure, as usual), the third line just hangs down under the cowl and this is the fuelline that you use for filling the tank.
Now you ask: "isn't the fuel now goíng out through the carb intead of going to the fueltank when I fill the tank" -No! The opening in the carb is so small ,remember that you fuel it when the carb is at idle, that no fuel is going in that direction.

You might also ask: " When do I know when the tank is full"?
You notice it when fuel is comming from the silencer exhauststacks

Regards!
Jan K
Sweden