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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