If it is an EFI model it is inside the fuel tank.
buy a pump and drain tank only, do not run dry if it's fuel injection
Inside the tank, take off the fuel shutoff valve.
Best bet in any fuel tank leak is to have the tank replaced
for wire harness maintenance
Inside the tank.
This requires a custom built gas tank.
harley 883 fuel tanl vent pipe
Put some fuel injector cleaner in a tank of fuel. Replace the fuel filter and fix any vacuum leaks.
You must change fuel tank
That is a really tough question but it is 4 gallons of pure fuel you can have. I had 1 till i was 19 years old
Its probably not the guages its more than likely the sending units located in the fuel tank causing the problem.To fix the problem will require removing the gas tank and replacing the sending unit.