The teflon washers in the bobbin case sometimes helps. When I worked in a sewing factory, we always wound the thread twice around the guide when we were winding the bobbins to use. After the bobbins are wound, test the tread with your fingernail. If your nail sinks in easily or the wound thread seems a little spongy, it is wound too loosely. (spelling) The tread needs to feel a little firm. This can cause backlashing.