[DeTomaso] vacuum advance on Duraspark II systems

[SOBill at aol.com]

Lee,
 
Holley carbs typically have two vacuum ports: one above the  throttle plates; 
one below the throttle plates ( called "ported"  vacuum).
 
The one below the throttle plates has full manifold vacuum. Full  manifold 
vacuum is max when the throttles are closed and near zero at wide open  
throttle. If you connect this port to the distributor, you will have max vacuum  
advance at idle and whenever the throttle plates are nearly closed ..... as in  
cruising.
 
The one above the throttle plates has zero vacuum at idle,  the  vacuum 
increases as the throttle plates begin to open, and  then falls off again at wider 
throttle openings. If you connect this port to the  distributor, you will have 
zero vacuum advance at idle (which can make for a  smoother idle), normal 
vacuum advance at part throttle, and zero vacuum advance  at wide open throttle.
 
Modern cars, when they still had distributors used ported  vacuum.
 
Be aware  that this is a semi-religious subject.
 
SOBill  Taylor
sobill at aol.com
 
 



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