Most tension adjustments can be accomplished by using the top tensioner. That being said, if you want to try to adjust the bobbin tension there should be a small screw on the bobbin case. [On a 221 the tiny screw is on the outside of the bobbin case. On my 110 year old 127 model, the tiny screw is also on the bobbin case.] That is where I would look first. If you can't do it yourelf, try to locate a manual for your machine. It will surely tell you how to adjust the bobbin tension.
Susan
January 2010
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