My MG runs on slightly when I turn off.
What causes this?

not using 98 octane fuel is the biggy.

had a look into the manual for specs and even it states 98 oct minimum.

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Aussie Leyland, Aussie Factory, Aussie Mini S.

Really? I doubt it. On an old, relatively agricultural motor like the A-series, it will run fine on 91. Our 2001 turbo Volvo runs on 91.

More likely is a carb in need of a rebuild kit or a head that needs decoking. I would have thought.

Its also a build up of carbon on the piston, valves and combustion chamber. It glows red hot when the engine is running.

Then when you switch the engine off the glowing bits ignite the incoming fuel which would normally need a spark plug. This causes the engine to do another revolution, so more fuel is sucked in and ignited by the glowing carbon.

But the glowing carbon cools quickly and the engine stops runing on.

Strangely enough - the higher the octane fuel - the slower it burns. So using a higher octane petrol means that the glowing carbon isn't self sustaining. But its not the answer in its self.

Subject to ongoing controvesy - the use of Flashlube does stop a carbon build up.

Mike

Hey
Drexxle, the way I heard it was that when the mini came out and for a long time octane levels in old cars had been quite high, higher than now so now we have dropped the level but have brought out special fuels to raise it back up. This may not be true but it is something I have heard around the traps. I have also heard the carbon build up idea and that sounds totally plausible.

If your compression ratio is high, low octane fuel will cause run on.
I only use Ultimate/98, no problems.
Twice I've had to use 96, and it runs on a little.
Don't even ask about standard ULP

It could be coke build up. Try the water misting trick.

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Too many cars, and too little time.

WOW you guys are really onto it. Thanks

If it's a high performance engine build (big cam, head, carbs, etc) and it's NOT running on, your C/R is just too low.

Yes, I'm serious.

<edit> running on is so much an A series characteristic, the factory put a gulp valve in the intake manifold of some later motors so they got a lungful of fresh air when turned off.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

One day....One day

Or maybe as simple as idle speed too high?

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1969 Mini Cooper S MKII (1330)
1972 Honda 750/4 (his),1976 Honda 400/4 (hers)
1982 Honda CB1100RC (ours)

Really? Do go on.

This of course is a load of codswollop. The recomended fuel was "Petrol" unless you had a Cooper S in which case the recommended fuel was 100 octane. The Normal cars were designed to run on Super petrol which was around 96 octane. You could also run on Standard petrol which was about 90 from memory.
The thumbwheel on the 25D distributor is so that you can adjust the timing to suit different fuels.

there is a way to prevent it,

put your foot on the brake and have it in gear, slowly let the foot off the clutch as if you are trying to stall it then when u hear the car slowing/stalling switch it off, this seems to do the trick.

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http://www.ausmini.com/forums/viewtopic.php?t=71255

lower your idle setting for starters

most mini donks have had (over the years) a head shave or piston change & the compression ratio is now-days "generally" higher than needed (on average) & can cause it to run on if not using the highest quality fuel avaliable from the pumps, add to that a high idle setting & an over advanced ignition & you will have run on

soooo,,, pick any one (&/or combination) of the above & you will have "run-on"

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

most minis do it,my engine does,high comp,v power fuel,the wifes stock standard 1330 does it too,put in first and let clutch out when turning off,easy fix.

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First you get the money,then you get the power,then you get the Mini.

Just stall it everytime you switch the engine off. I've done it for years, no problems.

Matt's spot on with causes. Runs on with or without 98, with or without flash lube.

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Lillee - 1969 Morris Mini K