Daryl
The vacuum port is in front of the throttle plate so when the throttle is closed there should be no vacuum in the line until the throttle is partially opened, So at idle no vacuum, open throttle partially then vacuum goes to the distributor,
Depending on the distributor that was designed to be installed, the ports were drilled at different locations depending on when the distributor needed the vacuum, only the 70 and 71 USA models should have vacuum when the car is at idle.
BTW I am pretty sure I checked that there was vac in the line when above idle when we were fiddling with your fuel mixture adjustments.
Al Lieffring
66 230Sl
New blue top just arrived
new gas tank on order