A short run on this machine reminded me I hadn't refitted the battery fuse and a bit of wire I had used in its place while working on the wiring got shaken out on the ride, resulting in the ignition and lights running direct off the alternator and causing the stalling when I expected a tick over. Boyer ignitions can cause lots of kicking back under these circumstances, as they go to full advance when kickstarting.
https://youtu.be/KoMbxPI4ppI B.W.