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MG MGB Technical - running on

hi
i have a 81 le that runs on when turned of it has had a service and it is not overheating it is unleaded someone said you can buy a anti run on valve is this true
ron
R C Reed

Yes the MGOC or the B Hive sell them, also try running on VPower or one of the higher Ron petrols and adjust your Dizzy a nudge (mark position with a blob of paint before you start!! so you can find a known point quickly)
K Harris

And get your idle speed as low as possible.

Charley
C R Huff

hi
thanks for your advice i will try that first
ron
R C Reed

A way to stop the engine without shaking the car to bits is to engage the parking brake firmly, right foot on brake pedal, left foot on clutch, engage 2nd gear and as you turn off gently lift clutch and stall engine. Much kinder than letting it shake about.
Mike Howlett

RC,

Also, do an archive search. There is a world of advice there since this seems to be a common problem with quite a variety of causes and solutions.

Charley
C R Huff

thanks
ron
R C Reed

Revs is crucial, but while mine always tended to do it it got much worse on unleaded, and turning the idle down was no real help as the engine really shudders and stalls if it is too slow. And this is with 97, 98 and 99 octane fuels.

The MGOC *do* sell an anti-runon valve but it mad absolutely no difference to mine. I suspect this is because is has to be Teed into the servo hose, if it could be mounted directly on the inley manifold I suspect it would be more effective.

I *hated* stalling it on the clutch, so plumbed the MGOC valve in differently so it emulates the American anti-runon system which is 100% effective. Now I can run an idle of about 800rpm which is nice and smooth as well as avoids stalling in traffic on long holds. See http://www.mgb-stuff.org.uk/wn_fuelframe.htm and click on 'Running on'.
Paul Hunt

hi paul
thanks, that was certainly some info sheet i will have reread it a few times to digest it all
ron
R C Reed

I find blipping the throttle as you turn off the ignition avoids the juddering run on.
c cummins

Hi thought i would add to this thread, for no reason and out of the blue my car started running on and on backwards forwards the lot.I am sure that some nights i could hear it kicking over this went on for months so i started looking through the threads for some knowledge? and no shortage of information on this subject but no real solutions for a sure fire fix, then over the last few days it stopped just like that , what had i done the only change was the full tank of petrol i had put in from a small out of town garage his brew was 99 octaine unleaded it was funny because on my first visit to this garage he said "I get a lot of classics here" well he has got one more now, so no more BP ultimate crap for me . so in short maybe change your fuel provider and you may just get lucky my friend.

Regard

Richard H

PS See your Essex boy the garage i now visit is located in Thaxted its the only one in that village so if ever your in the area give it a try
Richard H

hi Richard
yoy say the brew was 99 octaine do you know the brand name of the petrol
ron
R C Reed

Tesco sell 99 Ron (although a few sites have done by Trading Standards) because the 99 Ron turned out to be 95 Ron (But every little helps)
K Harris

Easist way to stop an engine running on, after turning the ignition off, put you foot down on the load pedal.
I run both my 64 B and 53 TD on Shell Optimax, or other high octane brands if Shell is not availabe, there is a noticable improvemnet in performance. Both MG's have unleaded heads fitted.
Bye, from a very frosty Abingdon on Thames
John Watson

"after turning the ignition off, put you foot down on the load pedal"

'Load' pedal or 'loud' pedal? If you mean the accelerator that didn't work for me either, and it was another thing I didn't like having to do.
Paul Hunt

Ron

I had this problem on my 72 Roadster, when I bought the car it had twin anti run on valves fitted. It still ran on, I tried changing ignition timing, mixture, higher octane fuel etc but to no avail.
In the end I was advised to push the accelerator pedal to the floor when turning the ignition off. I have been doing this for the last few years and it stops immediately. I have also removed the anti run on valves.

Paul
Paul

Thanks to everyone for your advice on the running-on problem. I'll start trying them out one by one to find out which one brings success

Cheers

Ron

PS Do any Essex Members go to any local Club meets?
R C Reed

I solved a severe running-on problem on a 63B by changing all the old engine seals and pipes, and carefully tuning it, setting the timing and the carbs to achieve a smooth and low speed idle. After checking the performance for driving, it now suffers only occasionally from very mild dieseling, mainly after being driven hard on a hot day (which its lady owner seldom does). The valve is not fitted to the air filter, but is left open to air (connecting it to the air filter causes the engine to stall.

It's a question of balancing the compromise between setting the timing for using unleaded fuel and avoiding running on. I suspect the margin for getting it to behave is extremely small.
dominic clancy

Dominic - which valve is this?
Paul Hunt

I can't resist adding my bit. The cylinder head on all of the BMC series A and B engines is a Weslake design and like it or not, the running on characteristic comes with as part of that design. It is not only MGs that suffer, it is all of the older BMC cars (Austin, Morris, Wolseley and Riley) as all of them use the same basic cylinder head design. I have been told that the problem is caused by the pointed section of the heart shape between the inlet an exhaust valves that heats up quite qickly and there is not sufficient cooling at this point to dissipate the heat. It is this hot point that causes both pre-ignition and running on. There seems to be some truth in this, as I have always when doing a de-coke or polishing exercise removed the point and rounded this off, with the result that running on disappeared on all but the hottest days or when the engine had been thrashed.
Chris Barrow

More or less what Porter says - and that was in 1984 long before the UK got unleaded and lower octane (although America did have them by then). He does say that later '12v engines' (his words) already had this modification as standard, which as well as reducing the point also lowers compression ratio slightly, both of which will have an effect on pinking and running-on. However this site http://www.flowspeed.com/cylinder-ident.htm indicates the American low-compression heads from 1972 had less point and a shallower combustion chamber, the latter counteracting the former to a greater or lesser degree as far as compression ratio is concerned. This also says the *block* needs a cut-out to make space for the lower movement of the exhaust valve on those heads.
Paul Hunt

Ron

I went to the South Essex MGOC meet a few times last year. It meets on the first Monday of each month at the 'Lodge Country Inn' at Rettendon near Battlesbridge.
There is a big turnout and it is a good venue.
It is difficult for me to get there too often as I do shift work. Then again it took me 22 years since joining the club to get there the first time and it's only 20 minutes away.

Any luck with the running on problem yet?
PR Hughes

Hi Paul
It stopped raining at last so I will try a few of the tips on the car today. I have just started going to that meet I live in Thundersley so it is close for me to get to. Hope to get some good runs in this summer.
I'll let you know if I strike lucky on the problem
Ron
R C Reed

Hi,

I think I may have solved my particular running-on problem. I tried a few of the suggested remedies and the best one I have found so far was turning the distributor back a notch. It's not 100% but a million times better than it was.

Thanks for all your imput, very much appreciated.

Ron
R C Reed

Retarding the timing is certainly what has to be done if you get pinking. It does result in more waste heat, but maybe the reduction in peak cylinder compression and the resulting hot-spots from *that* is reduced. However it also reduces performance and economy, which is a Bad Thing in my book. A properly functioning valve avoids that, and the fiddling about with stalling it and pumping the throttle, and should be 100% effective all of the time.
Paul Hunt

My early modified "B" engine in my MGA would contiue running on regardless of what I did.
I purchased an industrial Danfoss solonoid valve together with a 12 volt coil[catalogued in their range]the valve has a big .375inch BSP port, fitted this together with a flex. hose directly out the inlet manifold NO MORE RUNNING ON!
The solonoid valve is normally closed I supply power via a switch when switching the engine off to activate the coil and open the valve works like MaGic.
Cost for the importd assembly $80.00
t burnett

This thread was discussed between 28/11/2008 and 09/12/2008

MG MGB Technical index

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