Sounds to me like a bad ground, or a bad power supply to the fuel guage, most likely the ground. There are usually two wires that control the guage, not including the wire for the guage's back light. If you move those wires around and the guage goes from full to empty, you have a short there. This happens a lot on boats with electronic fuel guages. As far as the speedo goes, I just pulled the drawing up, the speed sensor is electrical, and comes off the drive axle. Most likely a short somewhere like the previous post said. If you cant find a problem up by the handle bars, Check where the speed sensor sits on the drive axle, there is probably a way to test the senson with a multi-meter, any respectable shop should be able to tell you how to test it, some may not want to, but if they are like that, find a new shop. Hope this helps, let us know what you find out.