We may have found other answers which could help you.
Click here for Machine Stuck Reversehow to get the tension right on my machine?
the thread is bunching on underside of fabric it looks like birdnest?
1965 Singer 275k sewing machine foot pedal?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
Presser foot is loose?
Engine revving up ?