Morris Minor Owners Club

who knows what about runnung on when the ing is switched off.

ive rebuilt and run in. london leeds many times {m1]

2000 miles already

things appear to be set right. and the engines a dream.


it just wont stop

This has only happened to me when the ignition has been too far retarded. But that doesn't help if everything, as you say, is "set right." So must also assume that mixture is correct.
Have you fitted the correct spark plugs? Has it been the same since rebuild?

This still happens to mine every now and then using 97 Ron Super unleaded (it's far worse with 95 Ron ) and it's never been retarded.Mind you it only lasts a few seconds at most. Adjusting the engine idle seems to help - the slower the tick-over the less likely it is to over-run.

Do you have an add on electronic ignition? I had a problem car once that would run on, but only if the handbrake was off. This won't be quite the same problem but might be related.

There was a backfeed onto the ignition circuit from the alternator warning lamp. This was enough to produce a spark and keep the engine running but with the handbrake on the warning lamp drew enough power to stop this happening.

95 is my problem i think. i shall try the 97.
i got this idea that the 95 would run cooler, may be the 97 is cooler.
its deffinatly ingnition due to temp i think. does last a couple of seconds but it feels painfull.
i am sure its the fuel, thanks chris.
no electronic ignition lowedb
i wonder if any of those additives may help

ive been using esso fuel

It might be worth trying a tankful of Shell Optimax or that BP stuff with a higher octane rating, to see if it does the trick, before buying Valvemaster Plus or similar.
Personally I prefer to use the additive with basic unleaded it works out cheaper than Optimax.

The higher the octane, the cooler the engine.....

Try the 97 then the 95 + Valvemaster Plus which will give you 98. See which combination you prefer then stick to that. I use 98 (Optimax) + Valvemaster plus to give 100 octane (with my 10:1 compression) and it still runs on a bit. Mind you I lift the clutch slightly as I turn the engine off to kill the run-on (with my other foot on the brake).

yeah higher octane fuel will help it to run cooler. .. wheres that page you showed me cam online that explains about octane ratings ? ... higher octane fuel can cope with being compressed more before it goes off spontaneously. the engine gets hotter when its going off before its optimum point ....

cheers
grainger

higher octane fuel can cope with being compressed more before it goes off spontaneously.

Also the rate of detonation following a spark is slowed with higher octane fuel - hence having to back off the ignition more when using low octane fuels (irrelevant for this run-on problem though)

I would guess that Brixtons newly rebuilt engine is getting very good compression - Have you done a compression test Mark? This would help identify higher than expected compression, especially if the head has been worked on (eg. if they skimmed it more than they meant to)

very interesting everyone. got lots to experiment with.
ive never added additives. i should look at a better position for ignition as ray mentions.
some times it feels like it fires backwards.
going to start with the higher octane.
probably not helping its temp stuck in londons traffic.

i am getting the feeling that my error is this backing off with lower octain fuel.
my timming must be sharp cos on the motorway its like a rocket to leeds, with no overheating.

if it is running on badly could it be that the engine is a bit coked up or you have a air leak. As the muck in the engine would glow after the igition is cut and cause the engine fire for a short while.

I had an engine ( not moggie) that ran on regardless of what was done, as a desperate last measure i removed the head and found that the head gasket was breaking down and all burnt. So I deduce that the head gasket was burning and igniting the fuel after the ignition was cut

Back in the old days when I used to read Practical Car Mechanics, I read that the "A" Series engine had a particular problem with the shape of the cylinder head combustion chamber.

The design is rather "heart" shaped (from above), and there is a sharp "peak". this can get hotter than the rest of the head, so that it can cause the auto-ignition.

if the head's newly cleaned/machined, it might just be too sharp!

Colin

Yes that 'peak' in the A series head is,or should be, the first thing
which is radiused off when the head is being worked on.

getting even more intersting.

Mark, is it not better with a slow tickover? Most times
the problem is caused by a tickover speed which is too fast
unless you have a tuned engine.

hi wille stuck in london, i keep the tickover as slow as pos.
i like this point about the "point" in the combustion chamber.
i must be like holding a hot poker in there.

Mark...I am surprised that a man of your experience hasn't
heard it before. I think it was designed to induce mixture 'swirl'
as it filled the chamber. You do not remove much metal, just
radius the point off so that it will not 'glow' so easily, certainly
worth it on a tuned engine. Then again, most of us have no problems
with run-on when using a standard A series. Let us know if changing
to higher octane fuel cures your particular problem for future
reference.

hi wille. i am not one for tuning. i like rebulding to the original, removing as little metal as possible.
( give way to dics brakes and radials though). this is certainly a small piece of metal that has a lot of thought gone into it, by the tuners. i suppose the unleaded fuel has brought the world of tuners into the world of restorers. got to move with the times. what goes on with the last of the a series minis?
does that still have the point?
shall change the fuel without adjusting the engine let u know what happens.
see ya willie (grand master) respect

i could say that "i knew that but forgot."
but i like the "you learn somthing new every day"