This spring when I got my motorcycle out, my gas gauge quit working as well. I put about 100 miles on it before deciding to take it apart.
I read online that sometimes the sender in the take gets funky and needs to be cleaned or a washer comes loose. I took it apart and it looked horrible, so I bought a new one from yamaha, for about $70 ish dollars.
Works like a charm now, but even with the brand new sender put it... It still takes quite a while to go from E to F after A fill up, so that is completely normal.