I ordered a spool of Aurifil 50 wt with my last fabric order. I know that it's an excellent thread but I wasn't sure if my machine would like it. Well, it did not! My stitches were horrible and I could pull the top thread right off my fabric with the tension so off. I was disappointed but then decided to watch tv and experiment with settings. After about 1/2 hr, my evil twin was ready to throw in the towel and some very unlady-like words filled the air. But, the good twin made herself a Black Russian and happily continued.
I made all kinds of adjustments and just kept playing with the tension dial, presser foot and trying an assortment of needles. Finally, I got some great looking stitches. On my particular machine, I had to set the tension dial about 1.5. Normally it's set at 4, so loosening the tension that much made the difference. I would never have thought to loosen the tension so much.
I also found that the spool fed much better from the separate spool stand behind my machine, rather than the vertical spool holder on the machine. Needles also made some differences, although slight. Schmetz Universal 90/14, 80/12, Topstitch, and Quilting #11
So, in summary: I spent about 1 1/2 hours (less a bit of sipping time) making adjustments, sewing samples and changing needles and making notes. Now that I have a great looking stitch I 'm ready to piece. Normally, I wouldn't have had the patience, but I just spent $10.50 on this spool of thread, and I was gonna' make it work! I found Blondie's words floating in my head, "well, heck shoot-fire, it worked!"