You should see a small screw on the flat/closed side of the bobbin case. Turning the screw a tiny bit counterclockwise will loosen the bobbin tension; turning it clockwise will tighten the tension.
Probable Causes: – Top or bobbin thread is not set correctly. – Make sure that the bobbin was threaded properly in the shuttle race. …
While lightly holding the end of the upper thread, slowly turn the handwheel toward you (counterclockwise) by hand to lower and then raise the needle. Pull on the upper thread to draw up the lower thread. Pull out about 10 cm (4 inches) of both threads and put them toward the back of the machine under the presser foot.
What tension should I use for cotton?
Cotton requires a moderate tension setting, usually between three and four.