OK Then. Checked it yesterday and low and behold The tacho is reading 1200 while my new digital laser thingy was reading 1900. 700 RPM!!! Difference.
The 3 year mystery has been solved
A huge thanks to all that have ponded this question on my behalf. The process of elimination has won out in the end. Very glad I didn't go down the governor dismantling track.
Drinking hot tea on a hot day is like banging your head against a wall
. It feels good when you stop.... "Terry" my dad.