Yesterday, I bolted the jointer down to a piece of 3/4" MDF and bolted the MDF to the table on my knee mill. I shimmed the MDF to make sure the knife drum was parallel to the mill table and took light cuts with a flycutter to true up both tables. They were both warped, cupped, and bowed. There didn't appear to have been a flat surface anywhere on either table.
After bolting the jointer back on it's stand and re-setting the knife blades, it works much, much better.