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You want it hooked to a port that has full vacuum at idle and subsequently cruising speed. When the throttle is opened, the manifold vacuum will instantly drop towards or all the way to zero depending on how far you stomp on it.


This can be misleading to some. If you just step on the throttle 1/4 to almost half way down you will still have a strong intake vacum signal when cruising. If you go past half throttle to maybe 3/4 then yes the intake vacum is dropping off and of course will drop to about 0 when at wide open throttle. I have seen it alot over the years when testing eng vacum for clogged exh systems and so on. And I dont mean it to be smart its just I see alot of people think as soon as you step on the gas a bit your vacum is dropping to zero which when you go right to almost 1/2 throttle the vacum drops a tad and then will stabilize at about the same vacum as intake vacum is at idle if you stay at that throttle posistion cruising along. Dont matter if its ported or intake as they are both intake vacum anyway just one is above the throttle blade and one is below. When cruising you usually wont loose the vacum advance until you go past half throttle or more when the vacum drops. Ron