Check for the following matters.

• Probable cause

  Adjustment of thread tension is not performed properly.

   

  Remedy

  Adjust the thread tension properly.

• Probable cause

  The threading on the machine is improper.

   

  Remedy

  Make sure that the threads are passed into the machine properly.
  Rethread the threads to the machine in an appropriate procedure.

• Probable cause

  Thread is tangled.

   

  Remedy

  Check the spool pin, thread holders, etc., and remove the tangled thread.
  Remove the tangled thread from the machine.

• Probable cause

  Differential feed adjustment is improper.

   

  Remedy

  Perform the differential feed adjustment with the differential feed adjustment dial properly.