Well, I finally managed to balance my carbs.
I was going to try Mr Gazza's suggestion of putting some plastic tube over the screw to help me aim the screwdriver but I couldn't get to it without removing the airbox & all that goes with it, so decide to have another go at it before I went down that route.
As I said previously, in my particular M750, a 1998, I could not get to see the balancing screw other than by using a mirror. This was because mine has oil heated carbs with pipes that have virtually no "give" in them at all, so I couldn't move the oil cooler out of the way and because of this I could not get into a position where I could actually directly see the screw.
It was a bit of a faff but it's done now.
Just a brake service, clutch fluid change etc, and a few other odds & ends, and I plan to tax it again from 1st March
Thank you to all who offered help & advice, it was all gratefully received.
Brian.