I owned a high mileage 1979 R100RT for awhile, one of the bikes I wish I still had in fact. I don't remember it being overly finicky, not any more than any other bike of that era. Bings can have sticky floats on occasion and the infamous diode board failure can happen. The diode board can be replaced with an electronic ignition set-up I believe, and the float height is easy enough to set.
The bike was an absolute mechanical rush / kick in the ass to ride though, I plan on getting another airhead as soon as possible.