I finally got around to washing it. On with the degreaser, hose it down, next day it would not start!
After checking the spark plug was dry I took of the points cover. About a half a teaspoonful of water ran out. In with the hair drier for 5 minutes, then she started first kick.
Now I didn't want this rigmarole every time I use the hose. The lead comes out of the points cover at the side. So if water gets in here it goes straight onto the points and can't get out as there is no drain hole at the bottom.