Stripped, cleaned and re-assembled the carb with a 're-build' kit from GSF. Plenty of muck removed, particularly from the accelerator pump. Now runs loads smoother, has lost that hesitance at low revs, much nicer to drive. Why I didn't just do this months ago instead of embarking on the sorry saga of the 'Empi' doorstop, I mean carburetter, I'll never know. Still, got a full refund without any quibble at all, wonder why?
Finish this cuppa, then back out there for new front brake shoes and wheel bearings.(German parts this time).