Thanks Gary,
Thanks for confirming - that's what I though as well, otherwise the point of vacuum controlled secondaries doesn't make sense.
Here a zoom on the linkage. They're identical on both carbs:
Focus on a diaphragm/vacuum actuator:
I guess diaphragms need to be serviced/re-calibrated or at least spring replaced? I have never worked on Holley with vacuum secondaries so will have to start understanding them
Ignore the crushed air filters, they have been unfortunately damaged while I was working on the car last week-end.