Vacuum at a single port will have the pulsating affect. Attached at the plenum will provide a more consistent "signal".
The better choice for a source for the vacuum advance is a "ported" vacuum port. That is, one that has no vacuum at "idle", but as soon as the throttle is "cracked", vacuum will be there. Look on the carb for a port above the throttle plates.
FWIW
Jim
Thanks for the reply Jim. I was wondering if that pulsating vacuum disturbed the signal to the distributer. I've read a little on ported vs. manifold for vac advance. Seems to me you wouldnt want vac advance at idle. I might end up advancing intial timing after moving to a ported source for the vac advance. Maybe I'll squeeze a little more vacuum out of this thing yet.
