Originally Posted by KULTULZ
I was going to try and stay out of this misinformed topic, but if what you say is correct, why does one have to remove the vacuum source to set base timing at recommended curb idle?
Researching the Venturi Effect will also answer a few misconceptions regarding vacuum signals.
Hallelujah, I second that. I will add to the confusion though
. Anymore, when I am doing a performance build that isn't a restoration one, I plug the vacuum can on the dist and curve it for full mechanical advance, adding the amount of initial that works. That helps keep from having to tune around different cams,etc. Just a little more to confuse...some Ford advance cans can be adjusted for both the advance amount and the amount of "signal" it responds to.
That would have to be some engine to achieve atmospheric pressure within the intake....it is negative pressure( vacuum), by the way.....and the reason manifold vacuum drops IS the fact that it is below the throttle plates. It is the spring rate within the can that over powers the signal as it drops and returns it to it's rest position. If it became the same as atmospheric...how would the fuel enter the venturis??
Now you can research the Venturi Effect as Gary suggested....