Duke,swapped out the B22 can with the 28 and wadda ya know? Idle is now stable @ 800 rpm's first time , every time. Vacuum is 15" @ 700 rpm. Guess it's just like the 13lb. rad cap. that always seemed to overflow until I swapped it with a 15 pounder from a '64. GM didn't always get right the first, but they figured it out eventually. Thanks
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Re: Duke,B28 did it
...happy to hear the problem is solved.
15" at 700 sounds high for a Duntov cam. Does the engine have a different cam?
In any event, given the +/- 1" tolerance to pull the diaphragm to the stop, idle vacuum was not quite locking the B22 can at full advance, and without consistent and stable spark advance at idle, idle consistency and/or stability is poor.
Don't throw away the B22 can. Many with base cam engines/manual transmissions could use it. There are a lot of wounded and dead vacuum cans out there!
Given your reported idle vacuum the VC1765 (B20) 12" can should also work. The 8" can is a little aggressive for your reported idle vacuum. If you get any transient detonation when lightly accelerating or on upshifting, the 12" can should eliminate or at least mitigate it.
Duke
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