dumb question, are you sure you had a manifold vacumn source and not a ported vacumnsource? Ported will show no vacumn at idle, comes up as you tip throttle in, and drops again under increasing or full throttle. Will show highest vacumn at state stgeady throttle and load conditions.
This was used to provide vacumn to the distrubutor (rather than manifold vacumn) so more intital timing could be added to improve fuel milage and drive-away performance on some vehicles.
Best bet is a port from below the throttle blades (look at the carb from the bottom and find one that you can verify), or go straight to a manifold fitting. I always make sure I have at least one manifold fitting just for this reason.
If you have no manifold vacumn at idle you either have a BIG leak, or WAY too much cam. Lowest i've ever seen idle manifold vacumn that would run (sort of) was 4-6" @ 700 on my old circle track motor. Is it possible one of the secondary throttles is hanging open??
Hope this helps, and good luck. :idea: :clover: