I recently wrecked my Yamaha vino and while I’m trying to replace some parts I thought I would fix the fuel gauge (which hasn’t worked since I got the scooter a year ago.) I took the sensor out to test if it floats in water and it does but, when I put it back in the tank the float sinks right to the bottom. I tried it again today and the gauge still reads zero and it doesn’t float. If I manipulate the floating arm the gauge will change appropriately. Any help would be nice and I’m always willing to answer questions!
You stated you tested the float in water. The problem with your testing method is, water is heavier than gasoline. This means the float could be buoyant enough in water, but not in gasoline. I'd suggest your float is bad. In most cases, you have to replace the entire sending unit, which includes the float, not just the float itself.