<VV> Re: YH Vacuum Advance?

[Mark J. Murphy]

This is the port/plug I was referring to, located (on an installed carb)
just to the left of the mounting stud that is closest to the "firewall"
(roughly 8 o'clock looking at the flange in direction of flow).  As you
described, this goes to a slot that lies across the throttle plate when
closed rather than fully before it, however (at least on mine) it only
provides 2-3 inches vacuum at idle and otherwise behaves as "ported" vacuum.
In my testing, this is not enough to significantly change timing at idle and
the vacuum signal follows the throttle rather than running inverse as the
manifold signal does.  The only possible detriment I saw was bringing the VA
in at the wrong time, which can be adjusted.  In theory it's really not a VA
port, but practice it works and has for a while now, at least for me.  Not
being a technical expert on Corvair parts I put it out to the list for
enlightenment.  Perhaps a better question for anyone who has been there
before me would be, now that it has been confirmed that this plug is a
normal part of the Corvair YH, is what is the down side to using this port,
and why is it not recommended?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      ,-----___\----,    Mark Murphy
      \--(o)----(o)--'  Derry, NH, USA
    http://m.j.murphy.home.comcast.net/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

----- Original Message ----- 
From: <FrankCB@aol.com>
To: <m.j.murphy@comcast.net>; <rsedman@earthlink.net>;
<virtualvairs@corvair.org>
Sent: Monday, July 26, 2004 3:02 PM
Subject: YH Vacuum Advance? Re: <VV> Vacuum, and the YH (Long)

>        If you examine the separable throttle body section of the Corvair
YH
> carb, you'll find that there is only a single shiny metal plug on the
exterior.
>  The hole that this plugs is NOT a vacuum advance port since it goes to a
> slotted opening in the bore which is PERPENDICULAR to the throttle plate.
So
> using this opening will provide vacuum even at idle since the opening is
located
> both upstream AND downstream of the closed throttle plate at idle.