Fuel gauge check

There should be metal fuel line from the sender to the carb which would supply a ground if it weren't interupted by a 3 inch piece of rubber hose.
The factory simply installed a clip on metal jumper from one metal line to the other.
You can creat a substatute jumper with a piece of wire ( flat wound or braided bare copper is best ) Held in place with a small screw clamp at each end.
Use an ohm meter to verify zero resistance from sender body to any chassis ground point. Once the ground is out of question we go back to " Sender or gauge ? "