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Re: Vacuum Advance - ???

To: <healeys@autox.team.net>
Subject: Re: Vacuum Advance - ???
From: "Bob Spidell" <bspidell@pacbell.net>
Date: Mon, 5 Apr 2004 22:29:36 -0700
Ryan,

There is an outstanding article on this topic by by Jim Hockert in the latest 
_Austin-Healey Magazine_.  This is one of the best articles on the subject of 
ignition and combustion I have seen.

In short, Healeys use a "ported" vacuum advance mechanism, which provides 
advance only under partial load; i.e. not at idle or at WOT.  This is different
from newer systems which typically use manifold vacuum.  Suffice it to say
there is enough of a vacuum provided by the airflow past this port at 
part-throttle
to aid combustion and fuel efficiency.


bs


ps.  _Austin-Healey Magazine_ is a publication of the Austin-Healey Club, USA.

********************************************
Bob Spidell         San Jose, CA        bspidell@pacbell.net
'67 Austin-Healey 3000             '56 Austin-Healey 100M
********************************************

----- Original Message ----- 
From: "Big Sixer" <healey@ledwith.com>
To: <healeys@autox.team.net>
Sent: Monday, April 05, 2004 6:35 PM
Subject: Vacuum Advance - ???


> On my HS6 carbs there is a small tube that sticks up where the vacuum advance
> line fits. I ran a wire down it to make sure it is open, however the vacuum
> which comes from there is neglibile. Any reason why? The tube goes down on the
> engine side of the butterfly valve, so there should be some vacuum force, but
> there isn't.
> 
> Also, when is the vacuum advance most in use? When it is idling? When full
> throttle and the most air is going through?
> 
> I don't get it: both why I don't have enough vacuum force and what it is meant
> to do?
> 
> Help would be appreciated.
> 
> Ryan





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