It may be that the gas tank is overheating. When you heat up gas, it expand significantly. It also emit more fumes that are a real fire hasard.
Check the air flow around the engine.
A worn piston can't force air, or anything, back to the fuel tank. If it leaks, you loose power, contaminate the oil with unburnt and partialy burnt gas.
Electro
June 2013
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