Have you fully cleaned and oiled the machine? This series can benefit from a dab of lubrication right on the peg in the center of the bobbin assembly. If this doesn't help, there may be some wearing on the inner bobbin assembly. They're made from plastic and the poly threads made marks or grooves on some of them that can catch the bobbin thread and create problems.
Last edited by Candace; 04-17-2013 at 06:18 AM.