Tracy, I would imagine you will need to take apart the tension and put it back together. It may have a set screw holding the big knob on. Then very carefully take it apart - photo or take note of positions, etc. Take a Qtip and clean the check spring with rubbing alcohol. Then clean each piece as you put it back. The old oil, lint and grime mess up a tension. Some manuals tell how they go but I'm thinking that generic doesn't. It is a kind of thing you have to kind of get a feel for it. Tammi has blog posts about tensions:
http://www.archaicarcane.com/fragile...-equal-stress/ &
http://www.archaicarcane.com/bobbin-...obbin-tension/ she has other info on her blog as well.