It varies. I've got 300 miles on mine and I've just started on my 4th jug of gas/oil mix. so maybe 90 MPG, but that would include the crappy economy it was getting while I ran 16:1 at the first.
Couple of weeks ago (the days are getting shorter so most my riding is on weekends now) I filled it up, went for a 25 mile ride, then refilled it with a measure when I got back Just about 750 ML for the 25 miles. This works out to 126.5 MPG.
Like Miles would say, "I'll Allow It!"