Fuel leaking from the throttle shaft on a Carter B&B (Ball & Ball) carburetor is a common issue that typically indicates the carburetor is flooding.
When there is too much fuel in the bowl, it overflows into the carburetor throat, hits the throttle plates, and then seeps out through the sides of the throttle shaft. While a worn (loose) throttle shaft can make the leak more visible, the root cause is usually a failure in the fuel level control system.
Common Causes for Flooding
Dirty Needle and Seat: Small pieces of debris can prevent the needle from seating fully, allowing fuel to flow into the bowl non-stop.
Incorrect Float Level: If the float is set too high, the fuel level in the bowl will exceed the height of the internal discharge tubes.
Leaky Float: A brass float with a pinhole will take on gasoline, lose its buoyancy, and fail to close the needle valve.
Fuel Percolation: On hot days or after a long drive, engine heat can boil the fuel in the bowl, forcing it out of the vents and down the throat
