Last weekend I went round and round trying to be able to machine quilt with variegated thread on my 503a. The upper thread kept breaking down near the free motion foot. I had the tension at 0 and it would still break. It seemed like the tension was ok when pulling the thread through the tension disks, but somehow by the time it got through the needle it was too tight.
The thread label says "YLI Machine Quilting 100% long staple Egyptian cotton" and I was trying to quilt a sandwich that was batiks top and bottom and Dream Cotton inbetween. I had the same thread in the bobbin. I'm not good at FMQ, although I've done some mostly I've used a walking foot.
I did all the usual things - new needle, cleaned every trace of lint, rethreaded everything. I tried both the FMQ foot and a walking foot. I loosened the bobbin tension a little bit. The thread continued to break. Eventually I took it to a Sew & Vac (I was at a sewing retreat) and the owner diagnosed the problem as the thread being too thick. She noticed that the breaks were occuring at the curves in the FMQ, but when I went back to the walking foot it still broke. So I bought new polyester thread and the problem resolved. The center of the quilt is done with the poly thread, I've got the binding finished, but the borders still need something.
My problem is I'm still longing to use this beautiful expensive thread (Mediterranean: blues to greens to purples) to finish quilting the borders. Does anyone have ideas on what might help me succeed with it?