We may have found other answers which could help you.
Click here for Singer Tempo 50
Singer sewing machine 626 kno?
the thread is bunching on underside of fabric it looks like birdnest?
Engine revving up ?
My CG 500/550 Singer Sewing Machine's bobbin isn't working?
Singer 507?
Singer zigzag 457 Stylist not threading bobbin/making stitch?