First, check that everything is as it should be. Don't assume that anything at all is 'right'. Check all the basics such as:
- Engine not running lean (too lean a needle valve setting, or too large a prop for the engine)
- Engine and engine mounts are solidly fastened and not causing undue vibration
- Fuel is fresh and has the proper nitro and oil content for your engine
- Fuel tank has padding around it, and fuel is not foaming up due to engine vibration
- Glow plug is of the proper type as recommended in the owners manual

Next, I would check the plumbing into and inside the tank. Can you hear the clunk rattle around? Perhaps the plane took a hard landing and the clunk flipped forward. Are the fuel lines OK, or are they nicked and leaking air? Is your muffler pressure line OK? Is the fuel line inside the tank OK? If it was nicked and leaking, then as soon as the tank level got down to the level of the tubing, the engine would suck air in and stop.

Always check the basics first (i.e., is the lamp plugged in?) before looking for the 'exotic' problems. The majority of the time, your problem will be something that you 'assume' is OK, such as pinholes in the fuel line (nah, that fuel line HAS to be OK. It couldn't be THAT simple, could it???)

Just a few ideas to get you started... I'm sure that others will contribute ideas too.

Bob