Originally Posted by Sewing Joe
My hunch is that there is a tiny piece of thread stuck behind the bobbin case base. The tolerance on a FW is very close, so it takes almost nothing to lock it up. Here's a link to a site with instruction on how to fix it. DO NOT lose the gib screw. It's tiny and easy to misplace.
http://thefeatherweight221factory.co...achineJam.aspx
Great link! I think the last photo on the page is exactly what the OP needs to look at. I had a similar problem when I took the plate off to clean the lint. I wasn't lining everything back up properly to sew.