No, if you added the shims, just leave them in place, nothing dramatic will happen,...sorry for posting late.
What I mean with applied vacuum is that the petcock only let gas flow down when there is vacuum applied to it via the vacuum tube in its back.
The diaphragms also work by the vacuum that they feel at the throttle of the carbs, lifting the needles and open the path to more fuel when that vacuum increases.
Hope you can solve this mystery soon
