Getting back to this a year later (or so). I checked the points and found them slightly off. I cleaned them with a points file, reset them, and adjusted the timing. That took care of the problem. For a while. It's been about a year and the cough is back. It did sit all summer again (second summer in a row) without being run. I would say i got a few months' worth of trouble free driving before the problem returned. Too busy to deal with it now but I will be getting to it soon.
