Thanks everybody.
I'm going to take it down to the Grandstand area of the TT course as there are lots of teams preparing bikes for next week's practices. I'm going to show my bike at all the other shiny, fast machines and tell it that it's being a slob and should get its arse in gear. Maybe that'll do the trick.
It's had a recent service (which I'd have done myself but for having few tools here at the moment) and at that a dyno run (as the mechanic was keen to sell me a Power Commander) where it showed 80bhp and a lean 'dip' between 3,000 and 4,000 rpm.
I think I'll find and check that sensor you mentioned but mine does have a choke lever rather than any automatic jobbie so is it still the case that I might have to?
Anyway, thanks again chaps. Still love my bike. Just want to know that all's well.