1. Adjust the presser foot pressure on the presser foot bar.
2. The dust on the feed teeth is thick; remove the needle plate to clean it.
3. The support screw of the presser foot bar may be loose; try to tighten it.
4. Turn up the machine head; there is a long axis connected to the feed teeth, and there is a tooth fork on the long axis to control the height of the teeth. Lift the small screw on the fulcrum a little bit, and put your hand on the needle plate to feel about two millimeters of convexity.
5. It is not very troublesome to disassemble and clean it. You can make a hook with a thin steel wire and hook it a few times from the push plate.
