Check your bobbin ... I suspect that is your problem..
The bobbin's steel case has a tension adjustment. It is a small screw that you can use the included tool or a screwdriver to adjust. To test the bobbin thread tension, remove the bobbin case and hold it by suspending the thread. If the tension is correct, the thread should unwind an inch or two. If the tension is too loose, it will drop too much; too tight, it won't unwind at all. Seems for most people, right out of the box it is set to very loose..needs to be adjusted before use.
answered 1 year, 5 months ago