I just picked up a machine at the thrift shop. I have another Singer, but the bobbin case is different on this one. It's a black plastic case that is removable and holds the bobbin. I doesn't seem to "seat" into the area it's in, and shifts around quite a bit when the top thread comes around it, causing the thread to jam up. I tried adjusting the top tension and the screws on the bobbin case with somewhat better results, but I had to go quite loose on both to keep the case from moving around, and the stitches aren't that great.

What am I missing?

Thanks