A question for the experts. I've posted before that I found a Singer 201 at Goodwill. It's all cleaned and oiled. It sews - excuse me - injects thinner thread beautifully. The stitch is tight and even. I guess it's called "balanced". Now that I have poly thread from Joannes, the thicker thread is a bit "loopy" occasionally when I sew on strap material. I've increased the upper thread tension to 8 on the dial and increased the foot pressure, and that helped. It seems that it sews really well at near "full speed", but if I go slower the stitches are sometimes loose on the top - the bottom is good. Do I need to increase thread tension even more?
The first picture is an example of the top stitching with the loose loops. The second picture is the bottom of the strap. The third is the Gutermann thread Im using - upholstery thread.
Any suggestions are appreciated.