At idle there should only be a slight amount of vacuum at the filler cap (or hose going to air cleaner).
If you have the original type valve, unscrew from the crankcase side (oil mist collector tube) and check.
A wild guess, normal would be 1 to 3 in Hg vac. (engine at idle).
Hope I get this right:
Stronger engine vacuum (idle, engine slow speed) to pull against spring/plunger (overcomes spring tension) to reduce flow.
Weaker engine vacuum (engine high speed) to pull against spring/plunger to increase flow.
Last edited by buoymaker; 09/10/2022 9:10 PM.
