Speedo79@aol.com wrote:
>
> Listers,
>
> My 1977 MGB has been slowly draining its battery overnight. I have >been
>checking all the possible switches when I got to the ignition >switch.
(snip)
> Also, what is the function of the running-on control valve? When is >that
>circuit supposed to be energized, and when is it not supposed to >be?
(snip)
Steve,
Actual name is the anti run-on valve. It's designed to stop the engine
from dieseling after ignition shut off.
The valve is connected to a power source that is hot only when the key
is turned off (slate/purple wire). The other terminal is connected to a
a grounded oil pressure switch, continuous only when there is oil
pressure. Therefore, the valve operates only while there is oil
pressure after the engine is shut off - about ten seconds. Through a
series of hoses and connections in the evaporative loss control system
(canisters, etc.), during the time that the valve is energized, vacuum
is applied to the top of the fuel float bowl which prevents gasoline
flow from the jet into the air/fuel mixture - and the engine stops dead.
Test the anti run-on valve by energizing the slate/purple side of the
unit while the engine is running. The valve should click shut and the
engine should kill immediately. This is a nice system to have
functioning.
The above information is taken from John Twist's Technical Booklet,
almost verbatim. I'll say it again - this is one of the best technical
source documents you can lay your hands on, particularly for folks new
to the MGB. You can find ordering information at
http://www.universitymotorsltd.com/
Don't mean to sound like a shill for John, but this is close to the best
$30 you can spend on your car(s).
Bill
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