After 50 or 60 years, cork carburetor floats are always dry and brittle. If it isn't already broken when you open the carburetor up, it will break when you try to remove it. At least, that has been my experience. So how to replace it? I have tried to find good quality cork to make new ones, but all I can find is coarse, poor quality cork which is unsuitable.
I found out quite by accident that cypress knees are extremely light but are tough enough to make excellent floats. This material is almost as light as balsa but is much, much stronger. Cypress knees are part of the cypress tree's root system. They grow out of the ground all around the tree and can be as much as four feet high. I've made floats out out of this material to fit Schebler carburetors. I made two sizes to fit 1/2 inch and 1 inch carburetors.
The float has a weak point which is in the middle where the screw hole is drilled. Also, the wood is cross grain at this point. I strengthened it by drilling a 1/8 inch hole across the float and gluing a 1/8 inch dowel pin in the hole as shown in the sketch.
I sealed the floats with gas tank sealer.