Fuel float in the carburetor, or fuel float on the gas gauge sender
arm in the tank?  The carb float is almost certainly available through
a dealer at the parts counter - have you tried?  They might have to
order it in from a regional warehouse, which only takes a day or two.

 For the gas tank, you are better off getting a complete sender,
because the rheostat for the gas gauge is 30 years old, and they do
wear out.  (Up, down, up, down, up, down...)

     --<< Bruce >>--