I take it you are actually referring to the Rev counter and not the Speedo - if so I had similar fluctuations n
ot related to power output or speed. This turned out to be the pick up (Faston) on the Ignition amplifier needing a bit of tension reapplying to the contacts.

Mine is on the LHD inner wing attached to the ignition coil just aft of the radiator and chassis oiler.


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2009 4/4 Sport Henrietta
1999 Indigo Blue +8
2009 4/4 Sport Green prev
1993 Con Green +8 prev