It's not just 66 bobbins that are a problem. My SIL got some FW bobbins at JoAnn's and they wouldn't work in her FW. She ask me to adjust the tension for her but it wasn't the tension, it was the bobbin. I had a 'real' FW bobbin with me and when I put that one in the machine, the tension was fine. You just can't use the 'remake' bobbins. They aren't to specifications.... wrong metal, or too big or too small..... they just don't work.
Does anyone know if the Sew-Classic FW bobbins work???