You most likely need to oil it more. It's common for these old machines to develop stitcky parts by dried up oil and grime accumulated over the years. You have to detect all oil points, apply a bit of oil to all of them, then run the machine a bit, move the stitch length lever up and down, a round of oil on every oil point and repeat a few times.
It can be caused by built up dust and lint under throat plate - feed dog and bobbin area. They often need a good cleaning too when taken out of long term storage. Slide the bobbin plate completely off, lift the lever slighly up and towards you and the bobbin case will come out. Unscrew the throat plate too and clean out all dust and pieces of thread.
All the holes on top of the machine are oil points, and there's several under the base and behind the face plate. Oil every hinge, joint and moving part that runs against another. Remember to oil needle and presser bar too, the area where they move up and down in the cast iron part can freeze up too.
Pay particular attention to the parts involved from stitch length lever to feed dogs. At maximum stitch length turn the hand wheel and they are easily detected. The end of the rods each have an oil point or two, as well as the moving parts under the feed dogs.
Last edited by Mickey2; 11-12-2017 at 12:59 PM.