We may have found other answers which could help you.
Click here for Sewing Machine Stitches TensionMy CG 500/550 Singer Sewing Machine's bobbin isn't working?
Singer 507?
how to get the tension right on my machine?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
Engine revving up ?
Need a service manual for a Singer Treadle Sewing Machine Model 66-1?