Ah! That explains it. I have puzzled by several references to "vacuum
retard". Every car I've ever owned has had a vacuum advance that actually
advanced the timing. I was wondering what people were referring to about the
vacuum and the mechanical advance working against each other. Now I know.
Thanks, Barney.
on 2/1/01 11:39 AM, Barney Gaylord at barneymg@ntsource.com wrote:
> 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
> application? ....
>
> 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.
>
> Barney Gaylord
> 1958 MGA with an attitude (and no vac Mallory dizzy)
> http://www.ntsource.com/~barneymg
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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