What should I do if the upper thread tension is too tight?
If the upper thread tension is too tight, loops will appear on the surface of the fabric. Reduce the tension by turning the upper tension control dial to a lower number. Also check that the bobbin thread was correctly threaded, as incorrect bobbin threading can cause the upper thread to appear too tight.
From the official Brother XH2149-001 Computerized Sewing Machine manual, page 1
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