I have the same thing on my 2005 RX-1. I even tried a new sending unit. Spent almost $50 on it and the same readings. Wasted $50 for nothing. When I fill my sled up, the fuel gauage goes to full. When I ride the gauge goes down twice as fast as it should. When it shows empty, I still have 5 or 6 gallons left. My dealer has no clue, and is waiting back word from Yamaha on this situation.