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Engine does not shut off (stop) immediately!


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Hello all!

 

I recently took everything (including distributor, etc), out of my engine compartment, cleaned and restored. Yesterday, I finally tuned the carbs, and started the car. Having completely yanked out the entire distributor, I had to also adjust the timing.

 

While the car is running quite smoothly, when I shut it off, engine does not immediately stop and goes huffing, puffing and rattling for at least 10 secs, then finally after considerable shaking of engine, it shuts off. Any idea what the cause of this anomaly might be?

 

Cheers,

Farid

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Hello all!

 

I recently took everything (including distributor, etc), out of my engine compartment, cleaned and restored. Yesterday, I finally tuned the carbs, and started the car. Having completely yanked out the entire distributor, I had to also adjust the timing.

 

While the car is running quite smoothly, when I shut it off, engine does not immediately stop and goes huffing, puffing and rattling for at least 10 secs, then finally after considerable shaking of engine, it shuts off. Any idea what the cause of this anomaly might be?

 

Cheers,

Farid

 

 

The engine is "dieselling" http://en.wikipedia.org/wiki/Dieseling , either the mixture is too lean or your timing is too far advanced. Or, possibly, if you have installed new spark plugs they are rated too "hot" eg NGK BP5HS instead of BP6HS.

 

What do the spark plugs look like after a run?

 

Andy

Edited by 67_gt6
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Agree that over advanced ignition could be the culprit. If it marginal depress the accelerator at the same time as turning off.

Electric fans wired directly can also cause the engine to run on after turning off as the motor generates some volts as it winds down.

 

Regards

 

Gerry

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Do NOT allow your engine to run-on (diesel) like this - it can cause damage.

With car ticking over and handbrake on, select first gear, raise clutch pedal until the clutch just starts to bite, then turn ignition 'off'. That little bit of drag should stop the engine immediately.

Ian Cornish

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When I bought my 4A new in Canada the engine happily dieseled at shut down. The cure was to run it on Sunoco 260 gasoline which was the fuel with the highest Octane rating at the tme. No doubt Sunoco 260 is no longer available, so, to reduce dieseling effects, the fuel with the highest octane rating should be used. This assumes that the ignition timing has been set correctly.

In the UK my TR originally used 5 star leaded (equivalent to Sunoco) with no dieseling, but supplies were stopped years ago. It now uses premium unleaded but it diesels.

If the dieseling still drives you mad Moss sells an anti run on valve, just like the one originally fitted to the MG Metro, which will stop the problem.

 

Tim

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Thank you all for the replies.

 

I tend to agree that the culprit might be advanced timing. Yesterday, I set my SUs; the front two were rich (the spark plugs were quite dark and wet!), and the other two, in my view, were correct (though the spark plugs were somewhat whitish.

 

Last week, since the engine was running little bit erratic, I checked the timing with timing light; I changed the timing slightly (must have advanced the timing by 2-3 degrees). I will test the timing tonight and see how it works.

 

Thank you all again!

Farid

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Whilst the anti-run-on valve certainly helps (I fitted one several years ago), I cannot say it is guaranteed to eliminate the problem. Which is the reason I continue to use clutch & 1st gear (as described above) to ensure that my engine does not run-on.

Ian Cornish

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Have you tried snapping the throttle open ?

Run-on is usually (if not always) caused by something glowing in the combustion chamber, could be an exhaust valve or spark plug overheating or even a piece of cyl head gasket intruding into the chamber.

Weak mixture or over-advanced ignition could cause this. White spark plugs sound suspicious.

I suggest checking the ignition timing, is the engine "pinking", is the distributor automatic advance and retard mechanism (centrifugal and vacuum) working o/k ?

/

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  • 4 weeks later...

If an engine is burning oil the carbon build up on the valves and Head ignites the fuel after the ignition is turned off cause the engine to run .

 

One time drivers added a shot or two of Red Ex to help disperse the carbon.

 

Only cure, is a head off decoke and re grind/ seat the valves. Standard practice every couple of years in the good old days.

 

Mike

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