Why is my machine suddenly so slow? Did I somehow key in instructions to go about 20% pace? I inherited this machine so I don't fully understand it

the easiest thing to do is to take it to a service center this is an advanced repair

Sounds like a foot control switch problem. Could be something as simple as a bit of something in your pedal causing it to not come up all the way, or a weak spring. If not this replacing the foot control would be needed.

Go to youtube and search for a video on Pattern dress making.
Cheers,
Embroidery Services
San Diego, CA

Do you have a speed limit switch on your foot pedal? My Pfaff does....
Cheers,
Kelly
Embroidery Services
San Diego, CA

Either the machine needs a drop of oil or you have problems with your foot control, the very worst scenario which is unlikely is the motor has gone faulty

it could be different things
have you checked to make sure the plug is correctly in the machine
one time I was sewing on my necchi electronic machine & it for some reason was going slow like you mentioned & so I started checking different thing & found the cord to the foot pedal was laying in side the foot pedal & it couldn't go any faster untill I moved the cord out of the way
it could also be the motor
& also the power cord & foot pedal
it's possible it needs to be serviced since it's been sitting up so long & since it's sewing at a snails pace

you can download a manual from here
http://www.singerco.com/accessories/instruction-manuals

in the search field type in W1409 and click "search" you can then download the manual for free on pdf.

Check your top tension dial setting is on 5, as this sounds like the thread is not in tension fully so is looping up around the rotary hook and not being held back by the tension device. Is the pressure foot lowered (this turns the tension on) fully and is the thread through the tension discs correctly. Lower the pressure foot and pull the top thread from below the tension dial, it should feel firm to pull, if it comes out easy, its not undertension, device could be faulty and machine will need to be serviced.

Also, check that the bobbin case is fully inserted into the rotary hook in the correct position, bobbin is in and rotating the right way and thread is into the tension spring fully.

If you have the manual pull it out, and carefully check the threading up instructions and follow on your machine - it is probably one of these things causing the jamming.

This site has a listing - http://pages.sewing-machine-manuals.com/173/InventoryPage/1340019/1.html

try taking the foot and the plate off and try threading it then get it going without the foot on and see what happens just got mine going