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Re: Distributor vacuum advance question - MGA

To: Rocky Frisco <rock@rocky-frisco.com>, mgs@autox.team.net
Subject: Re: Distributor vacuum advance question - MGA
From: barneymg@ntsource.com
Date: Fri, 04 Jan 2002 09:05:40 -0600
At 11:48 PM 1/3/02 -0600, Rocky Frisco wrote:
>Scott Willis wrote:
> >
> > It did not seem to make any difference so mine is unhooked. A local 
> mechanic said to take it off. I am also curious. Anyone know?
>....
>A vacuum advance is really a non-vacuum retard, since its function is 
>called into action when vacuum is lost and the "rest state" is supported 
>by full vacuum. ....
>
>When you use lots of "loud pedal" the vacuum goes down and the unit 
>retards the ignition timing. ....

Not for the MGA.  You are describing the system used on the late production 
MGB where the vacuum is ported from the intake manifold.  The MGA (and 
early production MGB) have the distributor control vacuum ported from the 
venturi of the carburetor, just upstream from the lower edge of the 
throttle plate, where you get effectively zero vacuum at idle, and maximum 
vacuum when the throttle is opened just a little.

>I think the best place for the vac advance line to come off is the intake 
>manifold; this is where my MGA and all of the Minis I've owned had it.

Stock MGA never had the vacuum tap on the intake manifold. - always on the 
bottom of the rear carburetor.

Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg

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