MGB: Running on

Hi
I took the 74.5 B out for a ride today - ohh what a nice ride - but when I came home and shut it off, it ran on for a little bit after shutting it of - just a few seconds maybe 2 -3 seconds total. This was the first time it has done this - anything I need to look into? If so what and where.

thansk for any and all help.

I though my old banger was full of carbon and I would have to live with it when it ran on since I had it.

But after a good tune, it turns off clean now.

I have changed the plugs, cleaned up and adjusted the points (last week) cleaned and adjusted the carbs, changed the air filters two months ago. Should I change / adjust anything else?

Are you using good gas? Sometimes my 79 will do that and it is usually a gas thing. One other thing to check is the antirunon valve, make sure the hoses are on tight.

Have you checked your idle rpm with a reference gauge? The lower the idle the less-likely to run-on.

Stop the car, put on the parking brake, shift into 4th, turn off the key, then let out the clutch. Being doing it for years

Where is the antirunon valve located?

[s]Don't know on a '69.[/s] On my '80 it's on the passenger side, mounted to the winshield washer bracket. There should be a hose connecting it to the float bowls on the carbs.

Should have said '74 - my error

Running on can be a sign of carbs being too rich. You said you adjusted them, but it might be worth revisiting them to make sure they're right. It takes a while to really get the hang of getting them just right - especially the HIF4s.

As others have said, check your anti run-on valve - the valve itself along with its plumbing. Do a google search for anti run-on and MGB and you'll find definitive step-by-step instructions for diagnosing and troubleshooting.

Good luck with it!

69's don't have a run on valve.

My error should have been '74

I believe my car to be set up totally as per spec. Only thing not oem is emissions stuff removed.
But unless I use premium gas 93 octane, it will run-on.

The Chicago MG Club has a wonderful technical article about this valve. If I knew how to send you the link I would. My computer knowledge only goes as far as replying to threads on this site. But I do know how to adjust the Weber carb on my 77 MGB.

I had trouble with my '77 running on, all the hoses hooked up etc... If the Chicagoland club website doesn't have it, I know there is a very good article that goes through how this thing works out there somewhere...

Sorry I don't recall where I saw it, but check the oil pressure switch on the firewall next to the heater box. Mine was sticking and never actuated the anti-run on valve. If memory serves me correctly the easy way to check it is ground the wire that is connected to the oil pressure switch, you should hear the anti-run on valve click and the car should die. You can try it with the engine off, but the iginition on, you should hear the click.

EDIT: I had it backwards.... Here is the text that tells how to test it correctly...

http://www.mgb-stuff.org.uk/fueltext.htm#runonna2


Be careful if you are going to replace that oil pressure switch, I found that the one from Autozone was backwards from the one on the car. If memory serves me correctly the one on the car should be open when you have oil pressure and the one from Autozone would close when you have pressure. If you put the wrong one in there the car won't ever run.

I used some carb cleaner (shot it up into the pressure switch (when it was removed) and just shook the switch until I could hear it rattle. Re-installed it and no more run on!

HTH..
Tony

[quote=applebj8]
I believe my car to be set up totally as per spec. Only thing not oem is emissions stuff removed.
But unless I use premium gas 93 octane, it will run-on.[/quote]

Higher octane gas is one way to cure the problem. Home Market cars never had an anti run-on valve setup because they never had to run the lousy low octane gas we're stuck with here! The low octane fuels and the emissions requirements made for a situation where run-on was much more likely to happen. Good tuning on the car should take care of it for the most part. The valve is easy to troubleshoot (when meticulously following a set of directions), so it should be easy to get it working again.

Good luck!