On-line problem of old sewing machine

This phenomenon is called spitting beads. The reasons may be:

1: If the upper thread touches a certain part, the tension of the upper thread will be affected, and it cannot be pulled back to form a small coil according to the original thread amount. This is mostly because the small screw of the shuttle spring is loose or there is a small burr on the top of the screw.

2. There is a wire head inside the wire clamping plate, and the two wire clamping plates can't get together, so the pressure to tighten the opposite wire is not enough.

3. The loose thread nail is not smooth, which makes the thread clamping plate slide inflexible.

Take care of these problems, and you may be all right.