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Tim Cole raises a very good point in the last statement of the above post. Check the plugwires and the rotor and the plugs to determine which are resistor type and which are not. IF too much resistence in the ignition system then it would be impossible to isolate any miss to one cylinder.

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So, if only modern cars have knock sensors, using 'shade nonsense' proven over decades before knock sensors might be the best course after all.

Tim,

Who was talking "modern cars" here. Why be so disdainful of a tried and true way to check to determine a possible cause of a "miss" AT IDLE.

The recommendation is to change spark timing with engine running and see if the "miss" gets worse with advance or seems to settle down with retarding the timing a bit. These are not even full degree changes.

Owen, thanks for chiming in. I don't think we're talking here about any kind of radical timing that would burn off the piston tops.

Question is, do you want to identify this "miss" as some kind of real problem, and if so, fix it, or do you want to put words in my mouth about timing issues?

Your replies are typical of the "experts", and therefore I must bow down...

But I've yet to hear from Drew on whether he did any checks on timing at idle.

I have heard no complaints from him on anything except a slight miss at idle. BTW, the low vacuum can also be caused by too much initial advance timing. I never suggested he advance the timing, except to determine if that made the "miss" worse, and if so to retard the timing until it smooths out... or not.

It's the simplest, quickest thing Drew can do now to eliminate one very good possibility.

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When did I ever recommend heavy detonation. Also I didn't ask a question, I made a simple suggestion that involved a timing test, not necessarily a re-set of timing, unless retarding the timing a touch smoothed out the idle a bit.

Please read a post more carefully if you're intent on replying to it, especially if your reply is intended to make the poster look uninformed

To recap: For the most part, it runs smoothly. Not as smoothly as you'd expect a 9-main engine to run, but smoothly enough. But intermittently it has a stutter, as if one of the cylinders fires every other time or two out of three times.

Because it doesn't do it all the time, I've had trouble running timing tests at idle (it seems to behave when I'm at home with my tools). The timing is currently set dead on to spec at 6? btdc.

DrewLA with all due respect,
My post on March 5th:
"Hi DrewLA, all the specs you've mentioned, and set the engine at were factory settings on a new car 60 years ago. Due to modern variables, eg: gas, age of engine systems, carb, etc., it would appear that there isn't much left to account for a miss that you are focusing on. If the sp wires are cross firing look under the hood at night, if you see sparking you found it. If you're really intent on finding a leaking wire run your hands over the cables as well as looking. . Try changing your timing to 4 BTDC. Sometimes you need to find what works on older systems, the parameters "set to factory specs" sometimes are used as a guide only to get the car started and subsequent adjustments plus or minus are needed to get the car to run as you like it. Maybe it's the nature of the beast or maybe not. Since it doesn't seem to cause any significant problems, any of your future options will be trial and error. Sometimes it's worth letting things be until other symptoms appear. Hope this helps."

FWIW: This poor horse has been ridden too hard and put away wet. With all the posts has anything really been solved?? Perhaps DrewLA you need to take the problem to a local mechanic that will be able to do what has been suggested by the posters on the website... who, in a concise and methodical way can check and eliminate all that can be an issue. There's been a large tome of experience and information given that tries to solve the issue: "To recap: For the most part, it runs smoothly" (not my words). Perhaps after all, it is "the nature of the beast".

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In a way, yes, much has been resolved (though not necessarily solved). I've run every diagnostic test suggested here, more methodically than most local mechanics would, and I have concluded three things:
-it's not something simple
-it's not something I've overlooked (experienced minds haven't suggested anything different than what I've considered)
-it's not worth delving into any deeper until it gets worse or there's another symptom

I'm happy leaving well enough alone for the time being, which is what I plan to do. Thanks to all who contributed their advice and guidance, I sincerely appreciate it.