The floats are usually closed cell polystyrene foam plastic - if the smooth outer finish of the unit is not 100% impenetrable, alcohol will enter and dissolve the walls of the cells making the closed cell construction open cell and it will absorb fuel like a sponge - it then becomes a sinker. It happens to carb floats frequently as the float is cast upon a metal arm. With the floats, the liquid enters between the float arm and the float material. Most fuel tank floats are captive on a spring hook - some Chinese fuel sending units have the float drilled and the float arm is simply a piece of wire bent 90 degrees, inserted through the drilled hole and held in place with a push on retaining ring. I replace sending units on Chinese scooters frequently for floats that don't float.
Shop Owner and Mechanic with over 50 years experience