Hi guys. Im about to install the engine(mds .18) and the fuel tank. I don't if I'm gonna need and overflow line for the tank. On the box says: "drill and use if it necessary" because it comes with port closed. And if do use it... won't the fuel leak when the plane is upside down or something. Please somebody help me out with this...Thanks.

the only lines I use in my airplanes are the fuel intake line and the muffler pressure line and ive never had any problems

I second what onytay said...I use two lines, the intake line and the muffler pressure line(for a glow airplane, that is...For a gas airplane, the pressure line becomes a vent line).

If you do end of drilling the port out and using it, seems to me that the muffler pressure wouldn't help the fuel get to the engine, since the tank would never pressurize.

Good luck!

The overflow line is not needed for MOST installations.

The reason to use the 3rd line (with a plug for while the engine is running, or you won't have muffler pressure in the tank) is a lack of access to use the carb line to fill the tank.

If you can conveniently pull the fuel line from the needle valve and fill the tank, you don't use the 3rd line. There are very few sport models that the .15 to .25 engine class would go on where you can't get at the needle for this purpose.

***
typos R us... [:'(]

?