Jon G - you are correct about the bores wearing. This is just one more instance where Carter was more customer-oriented. The first Carter vacuum pistons were brass. Carter found both the brass and the zinc alloy/aluminum bodies would wear; so the material for the vacuum pistons was changed to a soft alloy of aluminum. Thus the pistons were "sacrificial" but the bodies did not wear. Replace the piston, and back into original clearance specification.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop