I was having the same prob alot of the members were complaining about. I was reading 1/8 full when I had just refueled. I have the Yamaha guages in my cockpit.
Bottom line the fuel sender was shot. I called both Grady and Yamaha, and the part was not sold by either. I called a company called "Isspro.com" and they custom-made the part for my boat within a week at a cost of around a C-note. You can buy the after-market part made by Moeller for about half the price, but it is a half-inch shorter than the real deal. And, you have to go out and by a few other supplies to make it fit the other end of the wiring that goes up to the dash. By the time you go out and get the the hardware to make the after market part compatible with the guage, it may be worth your time just to get the custom-made part.
Bottom line the fuel sender was shot. I called both Grady and Yamaha, and the part was not sold by either. I called a company called "Isspro.com" and they custom-made the part for my boat within a week at a cost of around a C-note. You can buy the after-market part made by Moeller for about half the price, but it is a half-inch shorter than the real deal. And, you have to go out and by a few other supplies to make it fit the other end of the wiring that goes up to the dash. By the time you go out and get the the hardware to make the after market part compatible with the guage, it may be worth your time just to get the custom-made part.