I would say needle thread also. I find Mettler on the bottom and Sulky on the top works better than Gutterman on the bottom and Sulky on the top. Check your weights. I use a 70 or 75 needle. I think I use 37 or 38 with a 4.0 setting. Like somebody said once you get it right, make a note cause you do have to fuss a little. Also I find the slower I go, the worser it gets but too fast and I cant make the corners. I set my speed at half.