At 10:46 AM 2/1/2001 -0600, Rick Lindsay wrote:
> The original designs for vacuum advance used a port on the carburetor
that was connected to a small opening in the throat of the carburetor. ....
As the throttle is opened, the vacuum rises (depresses?) and the vacuum
advance module goes to work. ....
> .... Newer designs have a vacuum port on the inlet manifold rather than
the carb. That port shows pretty strong vacuum even at idle. My car has
BOTH ports. Which method of applying advance is BETTER for my engine and my
The method ported from the manifold uses a different distributor, which can
be thought of as "vacuum retard" distributor. The vacuum from the manifold
is high at idle and holds the distributor in a retarded position. When you
open the throttle the manifold vacuum drops, allowing the timing to
advance. You need to use whichever port is appropriate for your
distributor. Or conversely, for those who do not have both ports, you need
to use whichever distrubutor is appropriate for your existing port.
1958 MGA with an attitude (and no vac Mallory dizzy)