Changed needle and put on different spool of thread. I had a bonifide Singer needle, but decided it was the same size in length as a topstitching needle I had, so I went with that.
Interesting problem, which I think may have something to do with timing. It sews single fabrics just fine, but when I switched to two layers, it wouldn't sew in the center position. However, when I changed the needle position to the left, it finally decided to sew on double layers as well as single. Switched needle to right position, and it wouldn't sew a stitch. So now I have a machine that only sews a double layer when the needle is in the left position.
Anyone have that scenario before?