Hi.
The instructions of OS 120 surpass III say to leave a vent line of fuel thank without being conected to anything to allow the tank to breath (I think this is due to the pump so it does not require muffler pressure). One vent for carb, another to refuel and this one to breath.
My question is won´t the tank loose fuel from this vent during some turn or other maneuver? How do you conect those lines to prevent this (I have a 14 oz Great planes)?

Thanks Daniel Maia

One line goes from the clunk to the pump then the carb.
Another line is the over flow line. Also used as the vent line. It goes to the front top part of the tank inside
Third line is the fill line and should go to bottom front part of the tank inside. After filling you will have to plug this line or the fuel will run out. Also you can use this line to drain the tank by tilting the plane nose down.
With the plane right side up no fuel will run out the vent line. When the engine is running The pump sucks fuel from the tank and air is sucked in the vent line so no fuel will run out when the plane is inverted. Hope this answers you question.

I always ran the vent line to where it stuck up in the top of the tank. I then faced the vent into the slip stream. The fuel doesn't seem to want to come out much because the pump is sucking on the fuel and the slip stream is blowing in it even when in negative 'G' situations. If it did siphon, it wasn't much.

I never seemed to have any trouble.

Jim