Can't think of anything else.
Sewed 4" blocks together. Ironed them. Came immediately back to machine - sewed another 4" block together and when I lifted it from the machine my fingertips felt the bobbin loops they were so prominent!!
What the heck ....??
turned machine off, waited 10 seconds, turned it back on - still the same.
Adjusted tension from 5 to 6. Still icky. Removed bobbin, cleaned machine, oiled machine, replaced bobbin. Tension back at 5, still icky.
So I started sewing a bunch of "samples" to bring to my dealer and marked them 4, 5, 6, 7 - and all samples were lousy. I then set it to 3 for another lousy sample and the loops were ginormous (> 1/4"!!). Set it back to 5 and sewed another sample and ... it was good. Sewed several more samples and they were good. Set tension to 3 again and the loops were big but not ginormous like last time. Back to 5. Normal.
So did my machine just have indigestion or what?
Machine is Janome 6600.