i would suggest making sure that the bobbin is wound evenly and not to loose, when you insert the bobbin into the holder make sure that when you pull your thread to the right that the bobbin turns in the opposite direction. do check to make sure that the amount of tension you use goes with the fabric weight. there is also a little screw on the bobbin case you can tighten that screw a little at a time to apply tension to the bobbin.
nathaniel, January 2008