Originally Posted by 1.41

Check the bobbin area for jammed up thread. clean it carefully with kerosene and oil the race. This is a delicate mechanism that can get jammed up and freeze a machine.

Check both ends of the feed dog connecting rod. Page 58 of the Adjusters Manual. If there's any rust or corrosion at either end that could freeze the machine. Some rust remover and kerosene and even 3-in-1 oil to clean rust inside the connectors would work. If you use anything other than kerosene, make sure to flush the area with kerosene to get rid of whatever you use..

Check whether the stitch length lever moves. Take a look at whether the sliding block connected to the lever is jammed. If so, it can be unscrewed from the side and cleaned.

Check whether you have thread jammed up, wound up between the shaft and the handwheel.

Remember that the most important tool in the tool chest is patience. Use lots of it.

I'm sure you'll succeed in getting this machine working fine. Good luck.