I had pulled all my test equipment out to align my radio again;
So, I started my bike up and checked the output of the generator with my oscilloscope.
The output was rather spikier than hoped for into the negative, so redoing the rectifier was in order. Possibly the vibration was too much.
I finished up the latest revision of the regulator board, with a new Zener to bleed off any excess input voltage, a resistance across the input capacitor to bleed off any stored charge, a mechanically better connection to the board and some adjustment pots.