Today I received a quote from Treadwell Carburetors for that "check disk" - $21.00 ea.!!! It's smaller than my pinky nail, and each Model 29 carb I work on has two, which are destroyed during removal. That we know of, they're only available still from Zenith. Sheesh!
Work to the wise: check the operation of the check valves, and if they pass, don't touch 'em!!!
-Michael
