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What is this and what does it do?

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1st77mgb Avatar
1st77mgb Scott Mervine
Cleveland, OH, USA   USA
1977 MG MGB "Duthess"
1984 Ford Mustang "Maude"
Good evening all, I hope things are well with you and your family. I hope someone can tell me what this is and it function, thanks in advance.

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IMG_20170912_170222.jpg

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Anti run-on valve. Creates a large vacuum leak when the engine is turned off to keep it from dieseling...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

1st77mgb Avatar
1st77mgb Scott Mervine
Cleveland, OH, USA   USA
1977 MG MGB "Duthess"
1984 Ford Mustang "Maude"
That's was my first thought, thank you for confirming. Mines is not working, lol. Should be normally open and closes with power correct?

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balloonfoot Avatar
balloonfoot Lloyd Faust
Southlake, TEXAS, USA   USA
In reply to # 3590866 by dickmoritz Creates a large vacuum leak when the engine is turned off to keep it from dieseling...

Dick

not if its hooked up correctly............there is no vacuum leak. It creates a vacuum in the float chamber to prevent fuel from being drawn into the intake manifold causing the run on. The vacuum in the intake manifold is balanced by the vacuum in the float chamber....hence no fuel flow. Many times after all these years, they are not hooked up correctly and do cause a huge vacuum leak, but that's not how they were designed.



" Rules are for the obedience of fools and interpretations of smart men."
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riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
In reply to # 3590866 by dickmoritz Anti run-on valve. Creates a large vacuum leak when the engine is turned off to keep it from dieseling...

Yikes!! eye popping smiley

Scott,
The text book version of Lloyd correct response below.

B



Check your ego Amigo!



Edited 1 time(s). Last edit at 2017-09-12 06:17 PM by riley1489.


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Diver648 Gold Member Warren Siringer
Tucson, Arizona, USA   USA
1967 MG MGB
1967 MG MGB GT
1971 MG MGB GT
1974 MG MGB
See the buy, sell, trade forum if you want one.

Cubfloater Silver Member Jim Tice
Monroe, NC, USA   USA
1973 MG MGB
1973 MG MGB GT
1974 MG MGB
So how does one check to see if it is working? I have one 73 that shuts off fine and another that runs on forever.

Thanks,
Jim

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Simon Austin Avatar
The valve that shuts off fine....good

The valve that runs on....bad (or suspected of being bad)



"Speed costs........how fast you want to spend?"

Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, Ohio, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
When the key is switched off after the engine has been running, listen under the hood. Mine makes a distinct "pop" when it de-activates.

Electrically here is how it works.

There is a slate (grey wire) from the ignition switch that is normally hot (with key off) - with key on this circuit is depowered. The slate runs through an inline fuse and comes out spate/purple. Slate purple is connected to one side of the aro valve. The other end goes to an oil pressure switch near the rear of the engine on the right side via a slate/yellow wire.

The oil pressure switch is normally open (open with no oil pressure).

When you start the car there is no power coming from the ignition switch and the oil pressure switch is closed. Nothing happens because there is no power.

When you turn off the key there is now power and there is reidual oil pressure as the car spools down so the circuit is complete and the ARO ports vacuum air to the top of the float bowl as described above. When the oil pressure decays (the car stops dieseling) the oil pressure switch opens and the ARO closes (with a pop in my case)

To trouble shoot - pull the slate/purple from the ARO. With the key off there should be 12V power. If not check the inline fuse or wiring for a fault.

There should also be 12V at the oil pressure switch (slate/yellow)

Also using a meter check across the oil pressure switch with the car off. There should be no continuity. With the car running there should be continuity to ground.



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riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
In reply to # 3590943 by Cubfloater So how does one check to see if it is working?

Dan explained the electrical side of "how does one check to see if it is working" thumbs up so the mechanical verification is much easier.

With the engine idling simply block the ambient air intake, (lower large hose/opening) to the anti- run- on valve. The engine should stall.
If not check for perished hoses, loose clamps, etc. at the ARO valve, charcoal canister.

B



Check your ego Amigo!

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Thank you for correcting me, Lloyd...

Dick

In reply to # 3590910 by balloonfoot
In reply to # 3590866 by dickmoritz Creates a large vacuum leak when the engine is turned off to keep it from dieseling...

Dick

not if its hooked up correctly............there is no vacuum leak. It creates a vacuum in the float chamber to prevent fuel from being drawn into the intake manifold causing the run on. The vacuum in the intake manifold is balanced by the vacuum in the float chamber....hence no fuel flow. Many times after all these years, they are not hooked up correctly and do cause a huge vacuum leak, but that's not how they were designed.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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