Your sensor in the tank may be bad. Mine went out on me. Don't remember the cost but I do remember it was cheap. Two screws and a wire to disconnect it from the bottom of the tank. When the fuel level lowers below the sensor it looses contact, turns on the red light and cuts power to the pump. you acknowledge the light and flip to reserve and the power to the pump is restored. If you ignore or don't see the light the fuel will eventually run out of the carb bowls killing the engine prompting you to flip to reserve, returning power to the pump for the remaining amount of fuel. Even with my bigger tank the sensor is stock so it works the same, it just comes on later than yours. If your tank is near empty it takes about 20 minutes to change.
