What speed, dyno load and gear were you running when you observed this rich condition?
Also, after riding, do the finger up the exhaust test. Let it cool, then stick your fingers in there and run them along the sides. If your fingers are full of soot (fully black or chunky), you are running very rich. Lightly coated , skin very visible, is just right and yields good fuel economy. L/R tips should give the same reading.
39 mpg seems reasonable to me. I get 45-49 on my R80RT, depending on what I am doing.