Originally Posted by thepolyparrot
I think Candi is probably on to something. The invisible thread is so fine that if you try to sew with a needle that's too large or has too big an eye, the thread doesn't form a loop large enough to be caught by the hook. Skipped stitches.
Try a size 70/10 or even a 65/9 and see if that doesn't clear up your problem.
Since you can't adjust the upper tension, you may be able to compensate by tightening up slightly on the bobbin tension. Good luck! :)
I think you are dead on here Parrot! I should have added that needles seem to play a big role as minor as they may seem. Just to give you an example, I was using a universal needles in my featherweight and for the life of me couldn't get it to stop skipping stitches. I tried rethreading, changing needles, double checking that there was nothing wrong with the bobbin placement. I thought for sure it was the timing. Before taking in to be repaired I switched to a sharp just to be sure and it's been working fine now for weeks. Just that tiny little adjustment of a finer needle with the thread I was using and it runs like new. ;)