So my machine has steadily been refusing to sew knits for about a year now. It is an old, all-mechanical metal machine, and when I acquired it, it sewed knits like a dream. I always use either a ballpoint or a stretch needle and a walking foot, and I experimented with different thicknesses of needles when things started to go south. Basically, first the machine stopped zigzagging on knits (though it would still twin-needle). Then it stopped twin needling. And then it finally stopped stretch-stitching this week. In all cases the bobbin thread doesn't pick up the top thread so it just doesn't sew.
It is way overdue for a tune-up so I dropped it off at the only repair shop nearby today. I told the guy my problem and he told me there was nothing wrong with the machine since it still sews wovens just fine. He said "have you tried cotton?" I told him that the knits I sew are almost exclusively cotton and he looked at me like I was an utter idiot and said "Knits aren't cotton, they are polyester." *facepalm* So I showed him my daughter's cotton knit store-bought tee shirt and told him that was what I was sewing on. He is going to tune it up but maintained that there was nothing wrong with it since it sews wovens.
I am hoping that the tune-up will just naturally fix the problem but then this guy isn't exactly inspiring any confidence. And if it doesn't help, does anyone have any ideas?