Don't know if you are able to do this on your machine but, if you are, it is an easy way to get the tension right. Here goes. Make a sample sandwich and set the machine for a wide zigzag stitch and sew about 3 inches. Check out the quality of the stitch tension. Adjust the upper tension till you don't see the bobbin thread. If you can get it right with the zigzag stitch it will surely work for a straight stitch. If that doesn't seem to work, try one of the Magic Genie teflon washers in the bobbin case. I use one all the time, better safe than sorry.