Why isn’t my needle catch the bobbin thread?
First, make sure the bobbin-winding spindle (located on top of your machine) has been pushed back to the left for sewing. If it is not in the correct position, the needle will not go down and pick-up your bobbin thread. … If the timing is out, the needle thread is not meeting the bobbin thread in time to form a stitch.
A: Looping on the underside, or back of the fabric, means the top tension is too loose compared to the bobbin tension, so the bobbin thread is pulling too much top thread underneath. By tightening the top tension, the loops will stop, but the added tension may cause breakage, especially with sensitive threads.