I agree with Tartan. I had a similar problem with one of my treadles.....suddenly seemed to stop giving me the usual lovely stitches. It turned out that I had accidently used a spindle bobbin that even though at a good glance looked correct , it was in fact just a couple of mm shorter than the correct one. I swapped over and the problem was solved. I hadn't even noticed until another member of the forum in the vintage forum pointed it out to me....did I feel foolish! You bet!!!