XJ650 should be the same.

problem solved,
it was not the speedo drive,
a re-assembly error.
There is a curved metal washer that can be put back 2 ways, 'concave ' in or out.
the. 'incorrect ' way allows the other metal washer with 2 tabs to be not pressed in so the tabs do not engage properly and get worn down.
a ordered a new tab washer and inserted the concave washer correctly and all works fine. now.
I was aware of the concave washer, and having 2 choices but the parts manuals do not show enough detail to work out which way to insert