Anytime anything goes wrong with a stitch out, the first thing to do is to do a total re-thread. Remove both the thread spool and the bobbin. Replace the needle. Clean the lint out of the bobbin area. Check for burrs on the needle plate’s hole (where the needle enters the embroidery machine) and on the bobbin case. Rethread the machine with the embroidery foot in the up position, as this releases the top tension discs. Double check that the bobbin is in the correct direction.
If, after a total rethread, the bobbin thread does not stitch in the proper ratio (with the bottom stitching showing the center 1/3 bobbin thread surrounded by a band of 1/3 top thread on each side), then it is time to clean the bobbin case. If all else fails, then it may be time to adjust the bobbin tension. Bobbin tension is always the last thing to adjust.
When adjusting bobbin tension, always remember to write down which direction and how much the bobbin case’s screw is turned.
The video below has more information on cleaning the bobbin case and adjusting bobbin tension.
Cleaning the bobbin case and adjusting bobbin tension:
Still need help? Watch our videos on cleaning the bobbin sensor or cleaning the bobbin rotary hook and case.