Vacuum Leak at rear throttle shaft

[hugginjugs]

Carb#17058276. Rebuilt w/ cliffs kit using his recommendations. New bronze primary shaft bushings. 1978 Pontiac 400,de smogged, Ram air resto manifolds and complete 2 1/2" exhaust system. Shaker is open. Otherwise stock. I used recipe #1 from Cliffs book in anticipation of a mild cam in the future. Everything is working well. Maybe a little rich at idle but not horrible. Idle is not  smooth though and spraying brake cleaner at the secondary shaft causes a noticeable idle speed increase. Also smooths out. I searched and read several posts about this, but am still not clear. I see that cliff does not recommend bushings for the secondaries, but can install them?? Also not clear about the throttle plates. My leak appears to be outside where the shaft passes through the throttle body plate. Not sure how the indexing of the plates would have any affect on this. Again besides the idle the carb works very well.
Thanks

[omaha]

most of the time the rear throttle shafts do not leak. think about how often you use the secondaries compared to the primaries. But, that does not mean that they cannot wear. If you can visually see any  movement besides rotating type than there must be some wear. you may have to get in there and push around on the shaft to see if there is any slop. check for other things while your at it like warping or bad gaskets or maybe a crack. this seems like you have found the leak as you have narrowed it down pretty good. putting the bushings in is easy but getting the plates back in is a bit harder but it can be done. good luck!

[Cliff Ruggles]

The secondary shaft requires some play so the huge throttle plates can seat fully in the bores.  I would re-index, center and seat the plates.  Most likely one is xxxxed open slightly (vacuum leak).....Cliff