Featherweight help needed!
I think you've gotten some pretty good advise. The only thing I have to add is check the feed dogs to make sure they are operating. I had an experience where my Featherweight just stopped right in the middle of something. Like you, I checked for thread in the bobbin case, etc. Then, I called my son into the problem (he worked on sewing machines for 14 years). He noticed that the feed dogs weren't working after he'd checked the bobbin case, etc. for knotted threads. He took the bottom off the machine (lay it on its side, and remove the screw, very carefully. If you have the screw loose that holds the feed dogs on the mechanism that drives the feed dogs, it could be loose on the bottom the machine. That's why you need to be careful when you take the bottom lose. It's be very easy to lose that screw and you don't want to do that (if that screw is loose! If that screw is loose, the feed dogs won't move, or anything. And, while the screw goes in a little difficult place to get to, its not difficult to get it back where it belongs. and reinsert the screw where it belongs. Of course, this may not be your problem, but I had this happen just a week or so ago! Best wishes with your Featherweight!
Jeanette Frantz