While you wait for answers, we may have found some information which could help you.
Click here for Sewing Machine Repair Singerhow to get the tension right on my machine?
Singer 507?
What size needles can I use for my Singer 39a3?
the thread is bunching on underside of fabric it looks like birdnest?
Singer 201 went bang , smelt and now won’t work?
1965 Singer 275k sewing machine foot pedal?