I have a Singer 111w155 with a new Servo motor. I can’t get even, tight stitches. I’ve had loops on the top and the bottom and skipped stitches. I’m using size 69 thread and sewing through 2 layers of 3 oz. leather for the most part. I’ve noticed it’s better with thicker leather. The screw for the bobbin is so tight that I can’t move it. For that reason, I haven’t adjusted bobbin tension but, adjustments to top thread tension haven’t done much.