Lumpy ... it was lumpy .. so time to check the timing, valves and carb I thought.
Having cleaned the pulley wheel and repainted the timing marks I set the static timing and then with the engine running put it at 6dg, all good after i had adjusted the idle screw to increase the tick over.
I'm using a 123 electronic ignition so point gaps are not an issue ( although the proper advance curve is a mystery ..)

Then i tackled the valves, no problems here, one or two were very tight but now its all as 0.25 as per the book.
Checked the plugs and as they were a very light brown color i deduced it was running a little lean so I put a quarter turn on the air screw on the zenith anti clockwise ( clockwise more air less fuel, anticlockwise less air more fuel)
Last night all good, much less engine judder or vibration, reved up smooth .. great.

This morning drove the 12km down the mountain to the station, switched off the ignition and .. she ran and ran and ran .... did stop but only after about 30 seconds ...
My initial thoughts are, too much tick over so reduce that on the throttle screw or it's deg or 2 too advanced..
maybe 8deg would be better.
So in hind sight, my logic is that - having replaced the timing chain last summer ( full kit inc tension sprocket)
That maybe i set this a little off and so my 6deg could be like 4 to 5 & therefore way to advanced ..

I must say the drive this morning was very smooth, the uphill sections in 3rd gear felt a little less of a struggle that the day before.
I wonder how it will be tonight on the drive back up the mountain.

Has anyone any other thoughts on this?

Simon

Causes of "running on": Engine in need of a decoke, this is very rare these days with modern fuels and oils and can be ignored unless all other causes have been ruled out. Too fast an idle speed, as you already know. Ignition timing too far advanced. Does the engine 'pink' under load?

Nope no pinking ( that I could hear this morning ) i guessing as you that its a little to advanced and i have the idle too high to compensate.
Can't be a decoke as i did this when i changed the head gasket during the engine rebuild las summer.
I still cant find a answer to the electronic ignition though ... maybe the advance curve is not right here and the combination makes it worse
no one seems to know which version to use ( it's a 123 ) at 3000rpm it gives 8/10/12 or 14deg of advance ...

Running on would be an ignition problem,and my old 2a would do this now and then. Carbon build up was usualy the cause in older engines,bits of carbon still hot and glowing in the combustion chamber igniting the fuel despite there being no spark. I do not know about electronic ignition [been diesel for years] but check it is switching off properly. As it is running and driving well I would not rush to change anything yet. One thing is allow the engine to tick over for 10/20 seconds to cool some internally before switching off. Light brown is the colour you want on the plugs.

Just seen your post.I am slow at typing.

Can't help you with the electronic ignition, not enough experience with the nasty new fangled stuff... If this was my problem I would make sure the engine was idling at the right speed and retard the ignition slightly and see what effect that had. Also do a plug drop, see what the mixture is doing. I would have no complaints about light brown, if they had been black or even white that would have needed some attention.

Bit of redex in the fuel, clean plugs and a decent long run to clear the carbon. It can only run with the ignition off if it is getting ignited from glowing carbon in the cylnders, everyhitn esle is a distraction as its turned off. Don't take it apart to decoke, more trouble than its worth, just clean the plugs and give it a decent run. Plugs are the usual culpret as the carbon gets inside and stays hot. It is possible your plugs are too hot a grade but I wouldn't change unitl you are sure they are clean. Very common if you only do short runs.

Up date na closing this ... re adjusted the tick over at the carb to a normal speed ..
No more problems ..
Sorted

Simon Perks said:

Up date na closing this ... re adjusted the tick over at the carb to a normal speed ..
No more problems ..
Sorted

Click to expand...

Thank you for letting us know, it's very frustrating when advice is sought but the poster doesn't get back to us with results.
John

wrong grade of plugs can also cause this....getting very very hot.