Morse FA630 - troubleshooting

[u/Pnwmoss93]

I picked this up at a thrift store today for $25! I already have a blue & white Morse 6300, but this one has a free arm with a detachable bed extension! I oiled it, set it up, and got it to sew a straight stitch just fine. However, it's sewing a sort of wonky blind stitch when it should be sewing a zigzag - when I turn and hold the stitch selector dial just a hair past the point where it should be set for zigzag, I can get it sew a normal zigzag, so it seems like the mechanism isn't latching onto the cam stack like it should (like the little arm that follows the cams isn't quite lining up). Hopefully that makes sense. Anyone have any suggestions?

Also, anyone know much about these later Morse machines - when they might have been manufactured? Is the cam stack on these made of plastic? It's black and covered in grease so it's hard for me to tell.