seems after loading many bobbins with different thread. problem still there. If one pulls on the thread after it gets on the table one can pull for 6" or so then it's tight. pull it through the tight spot then it maybe Ok for a short time or it may pull erradic . We think it's ether the way the bobbin gets loaded or the bobin case . we have adjusted the screw, that makes no diff.
You are correct in suspecting the bobbin case as it could be that there is some dirt between tension spring and bobbincase casing or the tension spring.the piece that you adjust with the screw,is worn out,only way is to take apart and inspect
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