RE: fuel gauge
The fuel tank level sending units are not a Yamaha part. The Yamaha MF speedo's can except 3 different types of ohm values. A fuel tank sending unit is a pretty common part that can be purchased at any West, Boat US ect.
The easiest way to test a sender while its still in the tank is to remove the wire(should be pink) off the sender terminal. If the tank is aluminum it should have a ground wire attached to it. With the key on take that wire and touch it to the tank. The gauge should go to full. If it does the gauge is fine and so is the wiring to it. Then its the sender.
If the fuel tank is plastic there should be a ground wire attached to the base of the sender. Do the same test as above but touch the wire to the ground on the sender.
No........ the YDS software does not work with a carbed 2-stroke. HPDI's are the only 2-stroke that are YDS capable.