How do I know if my upper thread tension is too tight?
If your upper thread tension is too tight, loops will appear on the surface of the fabric. To fix this, reduce the tension by turning the upper tension control dial to a lower number. If the bobbin thread was incorrectly threaded, you may need to rethread the bobbin thread as well. (Page 1)
From the official Brother XH2164-001 Computerized Sewing Machine manual, page 1
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