I have bought the new couching feet and installed in onto my Sweet Sixteen. I tried it after watching videos and made sure my wool was loose but every now and then it did not catch when sewing. I did try a fine cotton but that would not catch at all so assume you need a thicker ply of cotton/wool to use. I tried a different foot but that did not catch at all so went back to the smaller foot and as I said with the thicker wool it did sew but every now and then it did not so was very frustrating. The tension on the sewing machine was okay as I checked that before starting the couching. What can I do to correct this or what am I doing wrong?