Manifold Vacuum Experiment

If I understand correctly........

Loose spring in can (CW adjustment less spring tension)comes on quicker and leaves slower with variations in manifold vacuum.
Tight spring in can (CCW adjustment more spring tension) comes on slower and leaves quicker with variations in manifold vacuum.

The adjustment is made so that it comes on quick enough for starts and good idle, but leaves quick enough so that the engine doesn't ping under light or heavy throttle operation.