The main reason it took me so long to work out was that I'd dismissed the possibility of a plug / cap as I'd reasoned (incorrectly) that it would still have run even if badly on 3.
Thumpers rule OK.......
A reasonable assumption, the old 400/4 being a machine with points I believe they would still run on one cylinder. I'm not sure if what happened with your 400 is the same with all electonic ignition machines, I know my Ascot will run on one cylinder (two seperate boxes on that), as will my superdream and as I recall my Divvie would go with at least one cylinder out. Like everything else guess, you live and learn.
