AJS & Matchless Owners Club

on the electronic ignition units if you reverse the wires from the pick up it changes the timing , see the link to the phason instructions (similar to Wassell unit )

My guess it that you have not always had the connections the same way round

http://www.pazon.com/files/PDF/PA2.pdf

It is essential that these two wires are connected the right way around for correct operation of the ignition system.
Reversed connections will give very retarded ignition timing.

Good guess but, except for one attempt on both clock and anti clock settings when I purposely swapped the wires round, they have never been changed and certainly were not changed before the last attempt.