Conference terri::cars_uk

    No, you are not imagining it.
    
    Overrunning happens when the engine can continue to fire without a
    spark from the plug. This can happen if the spark plugs get too hot,
    or if there is too much carbon deposit around. Some cars would run on so
    easily that the manufacture fit a solenoid valve to the carburettor
    to cut off fuel when the ignition is off (I think Vauxhall).
    
    Changing the fuel and timing alters the temperature the plugs run at.
    You may need to use different plugs or change the mixture (probably
    richer, which is no good for emissions, fuel economy or engine
    cleanliness) to fix the problem. You need to fix it - if the plugs are
    too hot then you could damage the engine. (Stopping the overrun by
    deliberately stalling the engine is not good practice !).
    
    You may also find that you need to use some leaded fuel to prevent your
    valves burning up. Especially if the engine is running with higher
    exhaust gas temperatures.
    
    Andrew

    .-1 is correct.
    
    There are two major causes of pre-ignition, timing and something hot
    enough in the chamber to continue igniting the fuel/air mixture. As
    pointed out, this is either carbon deposits, or hot plugs.
    
    I'm not sure it was a good idea to convert this car unless you have
    first changed the head to one suitable for unleaded. Have you done
    that? If not, I'd set things back ASAP or within a few months you'll
    have a written off engine. Whatever you imagine you may be saving on
    the fuel, will never compensate for that.
    
    Laurie.

    Dick
    
    	does the car still run on when using super unleaded, this is
    supposed to be of the same octane level as four star so I would imagine
    it would run on the original ignition settings.
    
    Andy

    (re .3) Super unleaded cuts down the running on but doesn't eliminate
    it entirely.
    
    (re .2) It is a conversion (new valves, guides, seats ...). I didn't
    just switch petrol.
    
    (re .1) The engine doesn't run particularly hot (at least now that I've
    got a thermostat that opens) but is that different to the plugs running
    hot? Is there such a thing as a "cool plug" I can switch to? As to
    there being carbon deposits - quite possibly, but I don't feel inclined
    to take the head off right now.
    
    (re .0) What about the theory that the advancing mechanisms are
    advancing too much (which means I'm having to idle with it too far
    retarded)? Has anyone see this happen?
    
    Cheers
    
    Dick

    
    I would strongly recommend you take the advice given in .2, else as
    stated you'll end up with a knackered engine. I don't think even using
    super unleaded will help as it's the lack of lead in unleaded that will
    cause the damage. You'll end up with damaged valve seating. There is a
    company who actaully remanufacture cylinder heads using special alloyed
    valve seats/guides if you really do want to run the engine on unleaded.
    The fact that the engine runs on, & on, & on etc. is probably, again as
    already stated hot plugs or the engine being really in need of
    decoking. My first car was an old Imp, which I turned off one day, took
    the keys out & went into the house. It must have been 5 mins or more
    that I heard it still turning over outside. Unfortunately it ran like
    a dog after being decoked as the coke sometimes increases the
    compression & helps with the sealing on knackered old engines. If you
    want the address of the company who will convert your head for unleaded
    mail me & I'll dig it out for you, else I think they advertize in FAST
    CAR or mags like that.
    
    Cheers.
    
    Ian...

    RE: -1
    
    I gather from .4 that he has done the head. In which case, I would also
    guess that he hasn't got old cokey plugs.
    
    I would firstly pose these questions to the people who supplied the
    head. It is unlikely that you are experiencing problems with advance
    and retard, unless you either replaced the dizzy/cam, or, the auto
    advance and retard is knackered. It looks to me as if it's timimg,
    and/or the plugs aren't hot enough. Again, the designers and builders
    of the head should be able to help with that.
    
    Laurie.

    Yes, I have the same problem of run on but mine doesn't always do
    it.....
    
    It doesn't even do it after some particular kind of run ie. long
    distance or stop, start journey...
    
    Any suggestions ??
    
    Bazza
    

    
    Aren't there some spark plugs with a V groove in the bended bit that
    are supposedly designed for unleaded fuel, NGK I think. It might just
    be a marketing gimmick though.
    
    Chris
    

    I think the plugs you mean are Nippon Denso (ND) V plugs.

If the head has been done, I would try a cooler plug before getting all worried.


What people say in here could be true, but I've been running my 1974 midget (us
spec with the lower compression ratio...8.0 instead of the 8.8) on unleaded since
I bought it last year.  It has never run on.  I put in some lead additive every
so often, but for the most part its just a good high octane unleaded.  Its very
hard to find leaded gas in the US now, so that's why I don't use it.

I would change the plugs and also be sure that the engine water temp is not too
high.  Mine runs at or below the 'N' mark on the temperature guage.

-Al

    Running on used to be a known problem on older A series engines.I had
    an 1100 and this used to run on badly.After making enquiries,I was told
    that BMC,(as it was then) knew of the problem.It was recommended that
    5 star petrol was used.I ran on 5 star for about 2 years with no
    problem,then I was unable to get 5 star and reverted to 4 star and the
    running on did not re-occur.The engine was correctly tuned before I
    tried using 5 star.The engine was also very fussy which brand of petrol
    was used.If Shell was used it felt as if the brakes were on upto 50
    MPH,all other brands that I tried were no problem.
    
        John
    

    The 1300 A series was notably worse than the other engines.
    
    The Maestro I had ran on, and 'pinked' quite badly at times.
    
    I would be very careful about running the older engines on unleaded.
    As previously suggested, even if you do, it may be safer to fill up
    with unleaded every 4th fill or so, just to protect the valve seats.
    
    Tim

    	
    RE.12
    
    	::The Maestro I had ran on,and 'pinked'quite badly at times.
    
    Can you describe to me what 'pinking' is as i've read about it in my
    Haynes manual,but they fail to describe what it is.
    
    	Novice:Andy.....
    

    
    
    I always thought pinking was pre-ignition, ie. the the cylinder
    combusts before the crank is in the right position for the piston to
    start it downward travel.  Thus the con-rod puts loads of strain on the
    crank because the cylinder burnt before Top-Dead-Centre.  It makes a
    sound like 'pink'?
    
    I'm willing to be shouted down though as I've been given several
    explainations by several people.
    
    Cheers,
    
    	Matt.

    Pinking is very difficult to describe, but, it only occurs when the
    engine is under load, such as accelerating fron 30 to 50 in top. It is
    a "rattle", obviously coming from the engine, that can be "switched" on
    and off with the go-pedal. It is not (normally) apparent when the
    engine is idling, or cruising. It often can't be heard simply revving
    the engine either. It's very difficult to describe, easier to
    demonstrate.
    
    Laurie.

    
    'pinking'... is the common term for the ringing sound that a poorly set
    up engine will make when under excess load.
    ie: when ascending a steep hill in 4th gear
     When the rpm drop below approx 2500 the engine will rattle (similar to
    a diesel), changing to a lower gear will increase the RPM and remove
    the noise. 
    
    Alan.
    

    Pinking is where the fuel detonates rather than burns. It can happen at
    all engine speeds and is most harmfull at high speeds when you aare
    unlikely to hear it. It is most audible at low speeds. Piston damage
    will finally occur. Some manufacturers (Saab?) played around with
    pressure sensors to detect and retard to prevent damage.   

    re .17
    
    Several Turbo cars have a knock sensor. This is because they are
    particularly liable to knocking. The extra fuel/air mixture blown into
    the engine raises the cylinder pressure before the compression stroke
    starts. The compression ratio of a turbo engine is normally reduced
    somewhat, but there is still a higher pressure in the cylinder at the
    end of the compression stroke when compared to a normal engine.
    
    Andrew