How flexible is your fuel tank? Lots of ARF's have fuel tanks which will hold pressure but lack the strength to keep from flexing. If you suspect that the tank may be on the wimpy side, try wrapping it with filiment tape and see what happens.

Your first post indicates that the engine runs fine until close to the end of the tank. That tells me that maybe it's not the engine but a tank problem. Are you running a fueling valve? If so, take it out of the system. Fuel dot and T fittings are much better.