Easiest way is to just stick a vac pump on the pressure reg vac pipe, with a pressure gauge attached, then see the effect of losing/gaining vac has.
The fuel reg has TWO diaphragms, if the top one is holed and so not responsive to vac signal this will have the effect, you have, fuel won't leak as bottom one still ok.
I would also check exactly what vacuum you do have, inacurrate valve timing will lose a lot of vacuum, or if running silly lumpy cams may not develop much at idle.
tabetha