I just purchased a 1986 Lesharo. When I took it on my first trip I was getting anywhere from 14 to 17 MPG. I got less in Minnesota and South Dakota than I did in Wyoming. Everyone I talk to says this thing should be getting 19 to 20 MPG. What should I be getting for a top end speed? I am getting about 70 to 75 MPH. I am going to give it a tune up this winter and change all the filters including the fuel filter. Is there anything else I should be checking. It has about 36,000 miles on it. Any help is appreciated.