Regarding 1976 Cadillac Sedan DeVille, 500 CI carbureted engine.

I wonder if my assumption that the vacuum unit should be airtight is correct. I
note that the rear choke pull-off vacuum unit has a built in bleeder which has
to be covered up when doing adjustments in order to keep the plunger
withdrawn--this is a bit puzzling as it introduces a constant leak into the
carburetor, although I
suppose the design factors in that much extra air. Could the heat riser be
similar?

Also, I wondered if I could simply install another vacuum unit (such as from a
cruise control servo, air conditioner door, etc.) near the heat riser and run a
beaded chain to the lever.

This seems to be an important feature for good cold drivability. Right now, the
car falls all over itself when acellerating while cold (everything else, acc
pump, floats, etc. seems OK and it performs perfectly when warm).

Tnx