I had the same problem with a Janome this winter. I was already doing leaders and enders and holding onto the thread behind the needle to no avail. Straight stitch plate didn't help. Changing to a new needle didn't help. Almost drove me crazy...until someone asked me what size needle I was using. I'd thought the size I was using was the right one for piecing cotton, but apparently it wasn't. Changed to a different size and the machine stopped gobbling fabric. I do still use leaders/enders, though
. Good luck-I know just how you feel. Be sure to let us know what solves the problem for you.