Well my friends, I stand defeated.
After spending 2 evenings going through every nook and cranny of the original ignition system on my 79, I have given up and just ordered a Dyna S from TIMS.
Problem was (and still is) spurious firing of ignitor 3,4 at 1,6 & 2,5 intervals, a form of cross talk.
Cross talk by poor grounding and / or the puny switched +12V wiring was suspected at first. Both these lines were reinforced with quality wiring, direct to the battery with no change what so ever.
Then the Honda HT coils were checked, found to be within tolerances (2.8 Ohms primary, 21.5 K Ohms secondary with resistive caps on) AND were changed as a matter of course with NOS, again with no improvement.
Next the trigger coils were checked. All 3 were, again, within spec at ~500 Ohms, all 3 producing nice clean pulses at their outputs to the ignitors.
Finally the ignitors themselves were removed from under the battery tray, disassembled, visually inspected (ugly), then connected up and set on the top of a stool next to the bike. With the engine running and my scope connected all over the place, I could not markedly improve the situation.
The final blow was when I discovered a tiny bit of spurious firing of ignitor 2,5.
This was the point at which I decided to accept defeat.
My take, the OKI units, all 3 of the old runny tar type have deteriorated to the point that they are no longer protected well enough from spurious electrical pulses, in and in proximity to them. May be some of the capacitors in the units have drifted or otherwise deteriorated, who knows. This is very consistent with the fact that the problem only manifests itself when the engine is hot.
So, time to focus my energy on my other trusty steed, my GL 1000, as the weather here is unbelievable!
And I do hope (and know, he is a great guy) Bill will not delay my Dyna S.
Hope I haven't bored everyone here.
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