I had a problem with my needle last week when doing FM. I happened to be in a class and the instructor tried. Turned out I had a very small nick - burr - in the plate where the needle goes down - sorry not good at the correct name for parts of the macine. Anyway, I could straight stich fine, but when the feed dog? was lowered for FM the needlethread would catch on the burr which was only exposed when FM. I remembered I had broken a needle a week or two before and I believe that was the source of the burr. Just needs to be fled smooth.