You can buy an instruction manual for the machine, in PDF format, online at the first link, below. These older Singer machines used a small universal type drive motor built into the vertical portion of the main machine. This was controlled by a footpedal rheostat, which could wear out, or oxidize over time. Most of the time, speed control problems can be fixed by cleaning or replacing the footpedal rheostat. You can try cleaning the rheostat with some aerosol contact cleaner that you'd get from an electronics supply distributor such as Radio Shack. Finding replacement rheostats is difficult, due to the low value of these older machines, but you can try various online sources. Sometimes, the connecting electrical cords are broken, due to being repeatedly flexed in use and in storage; it's sometimes worthwhile to carefully flex the cords while trying the machine pedal, to see if you can locate a break, which is suddenly "fixed" when you bend it "just right."
It's also possible that the motor or its friction drive is shot, due to age. You can remove the top cover of the machine, and look down in the arm (or look up from the bottom of the machine) to see the parts involved.
I'd try cleaning the rheostat contacts first.