• The upper thread could be installed incorrectly.
  Rethread the machine according to the instructions in the manual. 

Please refer to "Upper threading" of "Preparation" category.

• The upper thread tension could be set too tight.
  Set the tension to the basic thread tension setting or less.
  
  
• Make sure the spool of thread is installed correctly using the correct size spool cap for the size of spool.

One Point Advice   Place a spool of thread on a spool pin. 

• The combination of needle size, thread size, and fabric is incorrect.
  Be sure to use the correct needle and thread size for the fabric you are sewing. 
  (Example: Denim-size 16 needle and 40-50heavy-duty threads).

One Point Advice   Combination of fabric, thread and needle