Yeah, OS engines are allergic to plastic planes. Treat the symptoms with balsa.

Seriously, it sounds like you're not getting pressure from the muffler to the tank, and you've adjusted the idle to compensatem but as your tank empties the mixture gets leaner and kills the engine. Check the tank stopper, muffler, and pressure line for leaks and blockages. If you have a fuel filter fitted check that it's clean. When you're sure the pressure's getting where it needs to be, re-set your idle mixture.