There could be several reasons why the tension won't set on the machine.
- The upper thread could be installed incorrectly. Rethread the machine according to the instructions in the manual.
One Point Advice Upper threading
- Check the upper thread tension set.
- Remove the bobbin and make sure the bobbin is threaded properly in the shuttle race. Remove any loose threads or lint in the shuttle race.
One Point Advice Lower(bobbin) threading
- A needle is incorrect. Be sure to use embroidery needle(s).