I am a good friend of Ian (we actually originally bought the bike between the two of us) and am now looking at this issue again now I have sole custody of the wondrous machine.

As a bit more background and some more symptoms:

The snatching is most obvious to me now when off the throttle when slowing for a junction or the like and all but goes away when you pull the clutch in.

Chain tension has a big impact on the extent of the problem, the tighter the chain (keeping within the limits of course) the less noticeable the snatching and incidentally gives much cleaner gear changes as well.

If while coasting down you can keep some tension on the drive-line with a little bit of throttle the issue is less noticeable.

So far we have had a good look at the linkage previously mentioned (though not disassembled yet) and have removed all the rear suspension linkages and bushings for a clean and re-grease but to no avail. I'm about to free up some workshop space to have a good solid go at sorting this out as it is spoiling what is otherwise a very comfortable and smooth bike to ride.

Given the issue seems to be related to the amount and direction of tension in the drive-line I'm thinking a gearbox issue of some sort. It seems odd that it is fine under normal drive tension (i.e the force through the gearbox to the chain and wheel) but snatches with the tension in the opposite direction (i.e the rear wheel 'driving' the gearbox).

Thoughts and further advice much appreciated.
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Cheers.

Mark Bree