you are dead on with your mileage range for a 1981 650 maxim, i just got one and my first tank took me 92.8 miles before it started running out of gas, i flipped it to reserve rode about a half mile to the gas station and filled up.love this bike,just sold my mint 84´ v65 magna,loved it big time,but hated just giving my kids rides and taking it to work, that´s the only time i have to ride, this maxim works great for the little toolin´ around that i do.