Hi,
Put one of these in the fuel supply line (the one that goes to the carburetter:-
http://www2.towerhobbies.com/cgi-bin...?&I=LXD745&P=7
- or similar.
And connect the overflow / muffler pressure line to the muffler. Since you have side mounted your engine, the Pitts muffler will let the fuel drip out without it filling the muffler the moment the tank is full.
-David C.