Jim---Once again, thank you for your advice and suggestions. You have almost convinced me that I do not need to buy a new race hook assembly.
Your description of my most recent trouble says that the problem is usually associated with heavy fabric and/or very dense designs. My test stitchout of the butterfly is neither dense nor on heavy fabric. Just ordinary quilting cotton----the sample on the plaid fabric in the picture. And, I have used this design in the past with great success--on quilting cotton, 40 wt thread top and bottom, and with a Metallic needle. You can see this on the multi-colored sample I dug out of a drawer. So, I don't think what I have is a thread/needle problem. ( I posted 2 photos in Kathy's Hoop folder in the Photo section. For some un- known reason, I cannot get the 3rd photo to "go". It shows the same design on the same type of fabric same stabilizer and done with a metallic needle size 12. Just for comparison sake....)
I put my thinking cap on and came up with this question: Assuming that all of my preparations are "right"----no threading errors, Janome brand bobbin, same thread weights top and bottom, a needle type and size I know to perform well, adequate stabilizer and good hooping technique, a design that is not dense, suitable cotton quilting fabric, and all planets correctly aligned-----what else could be happening here?? My machine has not been bumped or dropped, it is securely fastened under a tight cargo net in the trunk of my car when transporting--it does not budge. And the only trips she has taken are to and from the repair shop!! No one else in my household has access to my machine. My cat is afraid of the machine and I don't even have a dog that might investigate the machine......I cannot think of any other variables.
Happy (?) stitching,
Kathy Strabel Camas WA