Tim - thank you, but carbking is no longer rebuilding carburetors, as the demand for rebuilding kits keeps him busy!
Michael - there are three possible reason why the carburetor is sucking air by the throttle shaft:
(1) the throttle shaft is worn
(2) the throttle body is worn
(3) both (1) and (2) above
The design clearance (you have to have some clearance or the shaft would stick when it got hot) is 0.004~0.006 inch. An additional 0.003 is not an issue. So you can use a dial indicator to determine the current clearance. If it does not exceed 0.009 inch you are OK. If the clearance is 0.010 or more, you will have idle issues; BUT it probably is fixable.
If the clearance is 0.010 or more, CAREFULLY grind off the back side of the screws holding the throttle plate to the throttle shaft(FAILURE TO DO SO WILL CAUSE MORE PROBLEMS!!!). Then remove the screws, followed by the removal of the throttle plate and the throttle shaft.
Use an inside micrometer to measure "out-of-round" of the throttle body, and a micrometer to measure out-of-round of the throttle shaft.
IF YOU NEED BUSHINGS AND YOU ARE NOT A MACHINIST: take the throttle body to a local machine shop. Bushings are available.
If you need a throttle shaft, you will need the inner number on the round tag riveted to the carburetor. A new old stock throttle shaft is probably available.
$350. is NOT excessive for a quality rebuild, but I WOULD expect a quality mechanical rebuild for that price. Still would not get you a "show quality" cosmetic restoration.
If you have more questions about the procedure - (573) 392-7378 (9-4 Mon-Tues central time).
Jon.
