Carter WCFB Vacuum Piston.
It isn’t unusual for the vacuum piston on the WCFB to become frozen in the cylinder where it resides. Be careful when removing the top of the carburetor that you don’t force things and break the piston lever. When the piston is frozen you may have to drill a small hole in the bottom of the float bowl, just under the piston and hammer it out. Use a brass drift punch. The piston is brass and can be damaged very easily. Once you get the piston out, clean, clean the cylinder so that the piston move very free up and down. We use a small bottle type of brush and spray silicon spray into the cylinder while we clean. The vacuum piston is no longer produced and can only be found as a NOS piece, or used. You may even have to resort to finding a used WCFB carburetor.