I need some help please. I decided to try treadling. My machine will sew a few stitches and than the needle becomes unthreaded. The needle is new. I have taken the needle out to make sure that the flat side is on the right, just like the manual says. I have rethread it and made sure that I threaded it right to left. Both the top and the bottom thread seems to move smoothly. The machine has plently of oil. I just had it service by a vintage repair man. Does anyone have any idea of the the problem could be? Kathie