I'm afraid sugar in the gas tank is a myth.

Sugar in the gas tank

This popular trick was recommended as a way to destroy an engine, causing great expense to the recipient of one's revenge. According to proponents of this act, the sugar turns to syrup in the gas, burns and melts, thereby destroying the engine.

The truth: Won't work! Sugar doesn't dissolve in gasoline, so it just sits there on the bottom of the fuel tank. The only way to stop an engine with sugar is to pour so much of it in the tank that the fuel pickup draws enough to clog the filter.