Does your machine have a single hole needle plate? that might help and if you have the "free motion bobbin case" maybe try that too. I have the Janome 6600 and use the single hole needle plate and the free motion bobbin case (it has a yellow dot) and haven't had the tension problem you are describing. UNLESS I try to go to fast then the stitches are longer and the bobbin shows a bit. Just an idea, hope you find a solution.