Air Bubbles In Fuel Line

Every line and filters from the sending unit to the carb needs to be checked.
Then pull the sender and check it as well.
If you have no air leaks in the line, then it almost has to be the fuel pump.
(Which by the way may be dumping fuel into the crank case if it can get air in the circuit)

Not trying to over complicate the issue, just solid diagnostics.