Checked every thing, re-checked & checked again, all O.K!
No 1 spark plug is sooty 2,3,4 are definitely at lot less! come to the conclusion that the valves are snuffed and lost compression.
When I bought the old girl she was gutless and after a compression test showed low compression especially on pots 2,3,4 which I put down to lack of clearance on the tappets and once re-set sorted the problem and has always gone like a good un since.
Will try and borrow a compression tester tomorrow but am nearly sure now that the head needs a re-con!