My sewing machine hates lycra. I'm trying to sew lycra with a zig zag stitch. In the best case, my machine will do a zigzag for a couple of inches, and then start skipping stitches. Sometimes it will skip all stitches on one side, leaving me with a straight stitch. In the worst case, it will not sew the fabric at all. This is what the worst case looks like:
The machine is a Pfaff 362 -- an ancient full-metal monster that I inherited from my grandmother. I'm using regular polyester thread, a regular foot, and stretch needles. I have tried fiddling with the upper thread tension, the lower thread tension, to no avail so far.
Any ideas that might point me to the right direction? The machine has been serving me well and chews through the thickest fur, and I'm perplexed that it would quit me now when sewing puny lycra fabric.