40 up a "long steep hill" sounds about right for a WD16H. Slightly retard the ignition on the advance/retard control to stop the pinking if you are convinced the timing is correct.
Thanks Keith I hadn't thought to do that. All My M21s have been far more sensitive to too much advance at low revs. The Norton seems not to need much retard at really low revs, perhaps it's engine is more sensitive under load. The last time I rode a 16H I was 17.....
Put in a Bosch M5AC. The previous plug showed signs of overheating
Starts fine and went up the same long hill at 45, from halfway up at almost full throttle
No pinking. Did not retard ignition. Engine seems more responsive hence 45 rather than 40. Happy