I have a 150cc GY6 Ruckus look-a-like scooter. A couple months into owning it the sending unit stopped working. After trying a new gauge I figured out that it was the sending unit not giving me the proper information. This is how I fixed it.
Philips Head and Flat head Screw Drivers
Socket Set (my bolts had a 10mm head on them)
A well ventilated area to work
A clean catch basin to collect the draining gas
fuel filter (optional)
Nitrile Gloves (optional)
First thing I need to get to the gas tank. My tank is located under my floor board and it is held on with 4 bolts and 2 screws. Your fuel tank location may vary. Once the floor board is loose the tank is now free fromt the frame. Unhook the wiring connector fro the sender. Also have a catch basin ready when you disconnect the fuel line to catch the gasoline.
Step 1: Removal of the sender
Use a flat head screwdriver to push on the tabs to turn the metal compressor on top of the sender. Once loose slip it off the wires, and gently lift until the unit is out of the tank. you will have to do a bit of wrangling since the arm and float are at an angle. Don't loose the rubber gasket underneath.
Now its out time to test and fix.