Rist horn repair

[Bob Olive]

On the subject of Rist Horns, does anyone have any idea as to the size of the points gap, and also how much clearance there is or should be - when static - between the face of the 'plunger' and the coil?  I have fitted a new diaphragm (the old one was rusted into 'lace'), and have plenty of electro-magnetic action, all the wiring is sound and tested electrically. When operated it will not vibrate as it should, despite gradual incremental adjustment.  BTW I have read, and been guided by, the excellent item on the Cornwall A7 site re Rist Horns. Any ideas will be welcome.
Thanks