I'd say that a carburetor is toast when there is too much corrosion in the internal passages, or the primary or secondary throttle shafts create a vacuum leak. A rebuild kit is necessary when gaskets get fused to the casting (not sure why we don't assemble them with oil?), or the pump plunger boot is torn, the rubbery pump plunger itself is worn-out, or the original leather pump plunger is solid with varnish (as in my case), or the secondary or AAP ('75) diaphrams are leaking. Otherwise, a carburetor-rebuild is just cleaning, and checking that things are in specification.
No one is making a new Choke Breaker for their rebuild kits? Both of mine are slight vacuum leaks. There is even a provision (torsion spring and slotted-linkage connection) for it on the end of the Aisan 21100-61012, the Fuji 'made-in-Japan,' and china-carb(s) choke-butterfly spindle/shafts, even though these carbs don't employ a Choke Breaker? The Choke Breaker is your lifesaver at the mechanic, or for anyone borrowing your keys who has little to no manual-choke experience. As, the choke button on the dash is basically operated either all-the-way-in, or all-the-way-out with engine vacuum itself adjusting the choke-butterfly to sit partly open just after the starter gets the engine running.
