I also worked on a yellow clone earlier this week. It was in very nice shape. Then I tried to sew. Something was wrong with the tension maybe. So I took a hard look. The tension unit was not seated into the housing quite right so I took it out - the spring was bent and not in the channel. Got that cleaned up and tried to sew. Nothing. So I put a nose plate from a working machine on it. Nothing changed. Then I checked out the bobbin case - it checked out ok. I traded it out anyway. Nothing changed. So I looked hard at the shuttle. There is a little spring in the shuttle and it was loose. I tightened it up and WOW that machine works wonderfully. It is very much like a new machine.