I have been trying to quilt using my old Singer 201, 301 and 15-91. I have the proper walking foot for these machines but when I get ready to quilt it seems like after sewing a block or so the walking begins to push the top layer forward and eventually causes a pucker in the line of quilting. This also causes the lines in the top to be skewed somewhat. When I turn the quilt over it seems like the stitch on the back of the quilt is kind of gathered like. I don't know if this is a tension problem in the bobbin or not. The stitches are perfect so I hesitate to bother the tensions. I have included a picture of this problem along with a picture of where I have the top pressure bar set. I really want to be able to quilt on these machines but I can't seem to find out what the problem is so I can correct it.