It sounds like there may be a burr or possibly lint build up in the tension spring. There were a couple of differences between the earlier and later cases. Perhaps
http://mysewingmachineobsession.blog...singer-66.html or
https://archaicarcane.com/model-99-a...-dog-cleaning/ or
https://archaicarcane.com/lessons-le...ing-the-twins/ would help.
Janey - Neat people never make the exciting discoveries I do.
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