Found this after I sent the email:
A nice diagram of the system with some more explanation:
http://www.mgdriversclub.com/tech/emission.control.general.html
Jeff
'70B
----- Original Message -----
From: "Jeff Fayne" <fayne@attglobal.net>
To: "Christian, Wellner L. CIV COMNAVAIRSYSCOMPATUXENTRIVERMD AIR 4.1.1.4"
<wellner.christian@navy.mil>; "MG Digest (E-mail)" <mgs@autox.team.net>
Sent: Thursday, January 08, 2004 7:33 AM
Subject: Re: 1974 MGB Died While Driving
> > Question: If I remember correctly, there is some kind of oil pressure
> triggered anti run-on valve on this car. Is the oil pressure switch (for
> the anti run-on valve) the one on the passenger side at the end of a short
> hose ???? If yes, is the switch activated by completing the ground
circuit
> or by breaking the ground circuit ??? I want to by-pass the switch in
case
> its some how activating at too high an oil pressure.
> >
> Here's my understanding on how the anti-run on valve works (Disclaimer: I
> have a '70 with out one, so I have no direct experience):
>
> While the car is running, clean air is drawn thru the vent pipe (bottom of
> valve) thru the charcoal canisters, into the engine via the rocker cover
and
> into the air/fuel mixture at the carbs as well.
>
> When the ignition key is turned off, the valve is energized via the
> slate/purple wire (+). The other terminal (-) on the valve runs to the oil
> pressure switch, which is grounded only when there is oil pressure.. The
> valve only operates for a few seconds (10?) until the presuure drops. This
> causes the valve to block the air inlet below the valve and connects the
> charcoal canister to the vaccum line going to the manifold. This causes
> vaccum in the system. Because this line ends up at the carbs air/fuel
> mixture, this vaccum causes them to restrict fuel flow, killing the engine
> quicker.
>
> My guess is that you can by pass this system by:
>
> - disconnecting vaccum line from valve to canister and leave open
> AND
> - disconnect vaccum line from valve to manifold and block
>
>
> >
> > Any other ideas ????? Anything at all. I need to get this car home and
> its about a $200 tow job away.
> >
> > Thanks In Advance, Skip
> >
> Hope that's it and this helped.
>
> Let us know what happens.
>
>
> Jeff
> '70B
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