Tuning

[markandsuefoss]

We've just got back from touring Ireland - 1200 miles without the hint of a problem, but a couple of problems have arisen suddenly. The car started immediately the other morning, just as she does normally, but then stalled. There seemed to be a slight misfire under acceleration (bit jerky) and she would stall when drawing to a stop e.g. at a junction. She seemed to be ticking over slowly, so just to get home I turned the tick-over speed up by ear and she seemed to run better after that, but when stopping and turning off the engine she would run on for a short time. I had done usual checks e.g. points gap and I cleaned the plugs. The ignition parts were new 3 months ago but I cleaned the plugs anyway. They were perhaps a little sooty, but not too much. Do you think she was running too rich and so the idle was slower?

[smithskids]

When you last filled up did you put the higher octane petrol in. I did a similar thing 2 weeks ago and had the same symptoms. Topped up withe the lower grade and it went back to normal.

[firedrake1942]

I had run on after fitting a recon'd carb and found that their was an air leak , allowing pseudo combustion to continue for a few seconds. Had the carb not been the main suspect, the PCV on the manifold would have been next as there was a possibility of the rubber diaphragm being perished.

The other thing I found contributing was that the choke cable was not allowing the lever at the bottom of the carb to return fully and thus it was running too rich.

Took ages to eliminate other stuff tho

[oliver90owner]

Auto detonation is not good for the engine. It can lead to broken rings, per eg.

There are several reasons for the situation to occur. Timing too late, weak mixture, wrong grade of plug, or carbon in the engine are a few of the important ones. Running far too advanced can also cause hot spots in the engine.

Check for excess heat somewhere in the combustion chamber by running at idle for several seconds before switching off. Not a cure, but a possible means of avoidance.

If your plugs are sooty, it is possible there is some carbon glowing sufficiently to cause ignition. You could try spraying water into the inlet manifold, with the engine at fast idle, to clear out carbon in the combustion chamber. That might tell you something if it cures the run-on. Be careful not to hydraluilic lock the engine (difficult on a spark ignition engine, but possible).

RAB

[dalebrignall]

redex down the carb would be a safer bet