86 Corolla Gas Mileage

I am having a problem with VERY poor gas mileage on my 1986 Toyota Corolla. My last fill up I got 300km on 40 litres. There is no way this car should be this poor. This is under 20MPG. If anyone has any suggestions I would sure appreciate them. And no, my gas tank isnt leaking.

Are you judging on what the Gas-0-Meter is telling you? Cuz mine, its says its on E when really its half full. Then when I drive it for a while it slowly starts to go up. then it goes back down. You just got to know you car if that may be your problem.