two. I have a O.S. 46 engine on a trainer and if I fill the gas tank all the way up I only have about 4 minutes of flying time before the engine starts sputtering and then quits. when I land it will still have about 3/4 of the tank left. any suggestions on what to do.

Check ALL fuel tubeing and connections and make sure you have the right tubes going
to the right places.

You might have the vent and the carb lines backwards.


Jimmy

Another thing to check is the brass tubing in the tank and the hose as well. If you have a pinhole or crack in either of them, it will pick up air when the fuel level is below that point and the enigine will quit. I fought this one for quite a while before finding the solution. Sometimes the easy solution is just to completely re-plumb the whole tank.

Check the pressure fitting on the muffler and the line to the tank to be sure that they are not clogged.
No pressure to the tank will create a vacuum as the fuel runs out and causethe engine toquit.


Happy flying, Oscar

What happens when the tank is not full at the beginning of the flight?

Try tuning the engine with little fuel in the tank.
It could be just too lean mix.

Check that the clunk or clunk line has not fallen off in the fuel tank.

I'll bet you have a pin hole in the pick line inside the tank like crossman said....replace all the fuel lines......I'll bet the problem is solved

How old is the plane / engine?
Has the combo performed well in the past?
Have you changed fuel?
How old is the fuel?
When you refuel do you have easy access to the carb fuel line to disconnect / reconnect?
How about access to the muffler line?
How hot is the engine's head after the failed flight is over? If it is real hot - lean condition that tends to end flights early.

Good news - you're getting pretty good at dead stick landings.

BTW - my middle name is "DeadStick" ...

I agree, this was my first thought also.

Put your finger on the exhaust pipe output and start it without the glow plug. Something could be clogged. I do this all the time with my nitro stuff.