Update

So six miles from home in torrential rain the Norton got fed up and decided to become a 414cc single instead of a twin. It got me home with some stress on my part, anticipating traffic lights and roundabouts to avoid slipping the clutch. It appears the left plug lead is the culprit, easily fixed after the rain had stopped. Oh and I remembered where the Guzzi keys were, the first day of Summer, hopefully not an omen!