I get between 185 and 200 miles (300-320 kms) to a tank. Stock FZ6 with a slight exhaust leak that everyone is jealous of (right Jeff?) because it has a great rumble to it.
I have gone as far as 60kms on reserve which is 37.5 miles.
I did have scorpion pipes for a few months, but my fuel mileage went in the tank (no pun intended) and I lost about 100 kms per tank in mileage. So if you want to keep the great fuel mileage, keep your exhaust system bone stock and don't mess with it!
Oh, and that big honking rear fender keeps rain and mud off your back quite nicely
