I changed the needle, changed the bobbin, changed the bobbin case, checked timing, and adjusted the tension. Nothing I tried came close to fixing the problem.
I was using Bottom Line thread in the needle and in the bobbin. This is a very high quality thread -- something that has been no-fail for me in the past. My machine has always loved this thread and behaved wonderfully.
I noticed as I was quilting that the thread would feed off the thread cone fairly evenly and then it would all of a sudden loop back on itself and feed through the tension disks. I had checked everything else and not discovered the problem. Was it possible that my problem was as simple as the thread not feeding off the cone evenly?
I surfed the internet looking for other quilters who may have had similar problems. I came across a comment someone made about using a knee hi to cover the thread spool to control the thread feeding off the cone. Someone else mentioned putting a bit of polyester batting in the first thread guide.
What could I loose, so I gave both suggestions a try. What do you know--problem fixed! I have posted a picture below so that other long armers who read this blog can have a look at the simple solution that worked for me. Hopefully, I can save someone else a week's worth of time should they ever experience the same difficulty. Note the placement of the batting in the first thread guide and the knee hi on the thread cone. Not the most attractive set up, but definitely worth repeating.
I am exhausted! It is surprising how much stress you put on yourself when you don't understand what is causing a problem. Once the job is done and you can relax, you realize just how tired you really are.
I am going to reward myself tomorrow by working on one of my own projects in the cool of my air conditioned studio. Ahhhhhhhhh.....relief from the heat wave outside!