I have a Davis Perfertion treadle sewing machine I know very little about. The serial # is 1978002. I would love to use it, but the tension is way off. Can any one help me? I looks similar to the Honeymoon & Exaiber.

If the tension is off, take it to a sewing repair shop. I've had my machine repaired many times and most shops were able to show me how to use it. If not, call a store that sells sewing machines and ask for help. They may know about your machine, or where you can get the tension repaired and more information.