The featherweight is an awesome little machine,but they can be a little bit twitchy. Lol. The bobbins are very short in comparison to other bobbins. As you have found out. I have found that if everything is in place and all the right parts are there, it runs beautifully. If not, well you know. I bought one without a bobbin case and bought a new one off of eBay. It never ran right, until I bought an authentic case. Have fun with it. Congratulations for finding the problem.