I have been using a Singer 15-91 and a Singer 201 for quilting Lapthrows. In the last several weeks, I notice that the top spool will jerk and if you continue to sew thinking the thread is wound too tightly in that spot then on the underneath side the bobbin thread is nesting. I have tried adjusting the pressure on the foot, changing the thread so that the bobbin is filled from the spool that is on top of the machine. Sometimes it will sew several rows before this happens. I really like sewing on these two machines but this is getting very frustrating. I am using a walking foot. I haven't tried piecing on these machines because I use the featherweight or one of the 301's and sometimes I use the new Singer 160 for that. Can anyone help me.