1.3 Engine running on problem

[PhilD]

My 1989 Maestro 1.3L has a problem with the engine running on. I knew of this when I purchased the vehicle, and thought that it would probably be due to carbon build up in the engine, as it is likely to have done a lot of short journeys with only 35000 on the clock in 19 years. I recently removed the cylinder head to de-carbonise it, but can't say that there was a very significant build up and the problem still remains.
My thoughts now are that the plugs are running too hot for some reason, because the electrodes do look rather white. I have checked and slightly richened the mixture as much as I can without making the engine run roughly. I have not yet checked the ignition timing, which I believe could be a cause of hot running, but would be surprised if that is significantly incorrect because there is no noticeable lack of power.
The other thing I wonder about is whether the engine in my current car is more prone to this problem because it is an unleaded version and I never experienced the same thing on my previous Maestro 1.3, which had a leaded engine in which I used Millers VSP additive.
Any thoughts or advice on how to solve this problem or feedback from anyone who has had similar experiences would be appreciated.

[E_T_V]

Usual causes are in some sort of order (most likely to least) are:
Incorrect mixture
Idle speed too high
Incorrect ignition timing
Carbon build up

Have a read through the A series tuning FAQ post I put up a long time ago (in the FAQ section).

[G Force]

Yes as above but, my thoughts would be that the idle speed is set too high as 9 times out of 10 this is the primary cause of running on when switched off.

Make sure also the choke fast idle cam is not dry and sticking causing the idle speed to remain artificially high, lubricate the cam quadrant with high temp grease.

Check the throttle cable has enough free play so to allow the throttle to return to the stop screw.


Gary

[PhilD]

Thanks for the advice. I haven't checked the idle speed with a tacho, but it is set a slow as it can be for the engine to idle smoothly, and I'm pretty sure it's no higher than it was on my previous Maestro.
This leaves the ignition timing as the only common problem I haven't checked that could be the cause. Would the ignition timing being incorrect result in the plug deposits being whiter than I expect?

[D87 SMW]

Possibly.

I think I need to back my timing off, as my 1.3 is idling too high once it gets warmed up. I noticed the temp light flashing, too. I've backed the mixture off but I can't go much further and the idle screw is right off as well.

[G Force]

Originally Posted by PhilD

Would the ignition timing being incorrect result in the plug deposits being whiter than I expect?

That is usually attributed to the carb mixture set too lean, But if you get brown spots on a white porceline plug nose that can be ignition timing over advanced.

If the engine idle is lumpy recheck your valve clearances.

Gary

[G Force]

Originally Posted by MaestroSpecial

the idle screw is right off as well.

Steve

That could be over advanced ignition timing, but just check that you have enough free play in the throttle cable and the fast idle cam is not dry and sticking.