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wjweiss3rd

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My wife's 1976 MG Midget continues to run, knock after she turns off the ignition. The former owner suggested (as hea had done) to add octane booster to the gas each time it is filled up. Does anyone else have experience with thios and what were there solutions. Appreciate any suggestions that people have tried.

Thanks
 
Adjust the timeing.
 
The run on or dieseling is associated with something being hot in the combustion chamber. Like Jack said, changing the timing can help. Pulling the head and de-carbonizing the valves and combustion chambers can also help.

However, if the car is otherwise running right, I prefer a simpler solution. When you're ready to stop the car, select 4th gear and as you turn off the ignition switch, ease your foot off the clutch. The engine will stop smoothly. This does not place any unusual loads on the drivetrain.

Regardless of whether you choose to change the timing, clean the head, or stall the engine, you don't want to leave the engine dieseling.
 
Some one or more reported use seafoam or something to decarbonize things with the engine running.
 
I think a '76 has a gulp (anti-run-on)valve. First, check your vacuum hoses and then use your Chilton/Bently manual to debug it. (I'd tell you how but the ones on my B's are long gone...)

I also find that mine will diesel if the choke is still on so you may want to make sure its coming completely off.

jlaird may well be right when he suggests timing. Make sure the timing is set right and the vacuum diaphragm works.

Good luck! Adam
 
Just replace the gulp valve as well. That's what it is supose to do.

Miss Agatha does not gulp, she is a lady. LOL
 
And what could possibly be better than a bug-eyed lady? Every time I see Miss Agatha I think of that Frank Sinatra song where sings "Make my eyes bug out my head..."
 
The Gulp Valve is a different animal from the Anti-Run-on Control Valve.

The Gulp Valve is suppose to reduce/prevent throttle lift exhaust back fires. It does this by opening when you lift you foot off the throttle. When this valve opens it dumps a large quantity of air into the intake manifold, leaning out the mixture quite a lot, and greatly reducing the likelihood of unburnt fuel entering the exhaust. Unfortunately, it reduces the effectiveness of engine braking. A Gulp Valve stuck open would make the car extremely difficult to start (cold) and once started you would not be able to make the mixture rich enough to obtain a smooth idle.

The Anti-Run-On Valve only operates when you switch the ignition off. At that point, it opens for a discreet amount of time dumping the contents of the intake manifold to the charcoal canister(s) and then the environment. The best part of this device is it has no effects on the running of the engine, because it only operates when you switch the car off. However, a malfunctioning one (particularly if it's stuck open) would have ill effects on an engine. The most likely symptom would be that you can not start the car even though you have correct static timing, valve lash, fuel, spark, etc.

I have both of these on my 76, and have to periodically check their operation due to California laws and regulations. When I switch my car off, I can distinctly hear a relay switch the Anti-Run-On valve on, and a few seconds later (no more than 30 seconds) off.
 
wjweiss3rd said:
My wife's 1976 MG Midget continues to run, knock after she turns off the ignition. The former owner suggested (as hea had done) to add octane booster to the gas each time it is filled up. Does anyone else have experience with thios and what were there solutions. Appreciate any suggestions that people have tried.

Thanks
Click to expand...

The only things I can offer up are: Check your mixture, and check your Anti-Run-On Control Valve.

I'm not sure about Texas, but all the fuel in California is now using Ethanol instead of MTBE for the oxygenate. The Ethanol in the gasoline changes how the fuel burns (slower burn rate (higher octane) but with less energy (less HP)), and as a result you might have to richen your fuel mixture a little to compensate. If yer knocking after switch off, that would seems to indicate that either the fuel mixture is too lean, or the anti-run-on control valve is not operating properly.
 
Cowboy's B is doin' it too... I've gone thru EVERYTHING twice but it still diesels on shut-down. Gotta get to the bottom of this. I suspected old or low grade fuel at first but now after a second tankful it still does the run-on thing. /bcforum/images/%%GRAEMLIN_URL%%/mad.gif
 
Nunyas,

Mea Gulpa. You are right - 2 different valves. In fact, thanks for the detailed clification!

I recognize the Riley Elf behind you. Was that picture taken at the Memorial Day Malibu run or did you encounter him elsewhere?

Adam
 
Rob - I think if you look closely to the anti run-on circuit you will find that what it is doing is applying a vacuum from the intake manifold, through the charcoal canister and the anti run-on valve to the float bowl vent line, which actually pulls the fuel back out of the jets. A very good article on the anti run on circuits is covered by Paul Hunt on his web site, the Pages of Bee and Vee at: https://www.mgb-stuff.org.uk/ On the home page, click on Spanners, then on Fuel and finally on Run on.
Cheers,
 
Adam58 said:
Nunyas,
...
I recognize the Riley Elf behind you. Was that picture taken at the Memorial Day Malibu run or did you encounter him elsewhere?

Adam
Click to expand...

That was at the Malibu Memorial Day drive. I was parked next to him while we were waiting to start the drive.

David_DuBois said:
Rob - I think if you look closely to the anti run-on circuit you will find that what it is doing is applying a vacuum from the intake manifold, through the charcoal canister and the anti run-on valve to the float bowl vent line, which actually pulls the fuel back out of the jets. A very good article on the anti run on circuits is covered by Paul Hunt on his web site, the Pages of Bee and Vee at: https://www.mgb-stuff.org.uk/ On the home page, click on Spanners, then on Fuel and finally on Run on.
Cheers,
Click to expand...

Ah, yes, I thought I didn't have the theory quite right! Thanks for the correction.

Now that I think about it, this lil tid bit of information may be why I've been experiencing intermittent run-on with my car. I've switched to a single HS6 and haven't bothered to connect the float bowl to the charcoal canister circuit, yet.
 
Nunyas,

Then we saw each other there. I was driving the '74 Teal Blue RD trying to keep up with that ^%%$$$ Elf throught the mountains and he and I were in the group that worked on the AH100 that quit at Hueneme Rd. Fun trip!

Adam
 
d'oh! We more then likely did! /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

I know I at the very least saw your car. I had the only Rubber bumpered B with the rubber bumpers still on it on the drive /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif
 
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