So new chain (KNC) fitted. First two rides were fine … But the chain was too long so I shortened it? I also twiddled the angle of dangle screw …
Now it jumps like buggery – but only really in the middle ring – I still have the unfashionable 3- and only in the of the rear gears….

Now, it could be rear cluster wear but as that has done less that 150 miles , I doubt it!
Any thoughts?
Could the angle of dangle adjustment do this?

Definitely. If there’s any jumping at the back end, that’s the first thing to check and correct, before fiddling with indexing etc.
Top jockey wheel is probably too close to the sprockets.

Yes

If dangle screw is too far in – mech is too far back – reduced wrap on casette.
Wind screw out (more visable thread at head end) to let mech swing forward.
I found that it worked better and better until it did not change down from the biggest sprocket, then I knew I had gone too far.

Stiff chain link?

Thanks all,
Not sure about the stiff link but I will go and stick it on the workshop stand in a minute …
I have wound the dangle screw out as the jockey wheels were almost touching the rear cluster

Look in the manual for your mech, it will tell you what adjustments you need 🙂