Depending on the year of your machine, the information in this adjusters manual for the 201 is likely applicable. Page 11 starts the troubleshooting of motor issues. Let me know if you can't get it with this link.
Edit: just saw yours is a '49. This adjusters manual should be very applicable for the motor anyway.
Singer-201-Service-Adjusters-Manual.pdf
drive.google.com
Edit: just saw yours is a '49. This adjusters manual should be very applicable for the motor anyway.