This weekend's adventure was a sewing one for me. I was doing a lot of zigzagging with newly-cleaned Rizzo (1950s? Universal). She worked great except for one problem: I would intermittently lose tension for the bobbin. In some instances, it looked like the thread would slip out from under the flat spring and travel along the side of the case. I'm not sure if the bobbins aren't snug enough in the case or what. I've tried tightening the spring, loosening it, trying different bobbins, slowing down, speeding up. Nothing seemed to help. I'm wondering if it might have some back and forth movement that is pulling the thread out of the bobbin case spring. Any ideas on what might be going on or how to correct it? She ran so well otherwise!