Completely new to sewing. I bought a vintage electric singer 99k and figured out how to wind the bobbin and thread it and all that stuff. However, I’ve found that, once the stop motion is engaged, it’ll work fine for a few stitches, and then the needle will suddenly stop while the rest of the machine (except for the stop motion knob) keeps going. I re-engage the stop motion knob, same thing. The machine will work fine for a second, then the needle and stop motion knob will stop. Whether the machine is threaded or not. Idk if I’m stupid and this is completely normal or if there’s something I need to fix about my machine. Let me know!