It is interesting, I was inquiring to my LQS who is my dealer for the Janome. ( I have a Janome 6500 memory Craft) about getting a different machine for doing quilting on a frame. They were telling me they did not sell any frame, I then inquired about getting a Janome machine for a frame I was thinking about. She was quick to ask why I would want that machine ,what would I gain, she said I would just end up with lots of tension problems... Hummm must be something with that machine because she said that to me right away. I have the Janome that I do the piecing on and love the machine. I have a Juki that I do the FMQ on and it was doing the loopy stuff to me, but seemed like it was a direction problem because it would not do it all the time while going down the run. I too put the feed dogs up and use the sil pad over the feet and that seemed to fix the loopy's. but it was a Juki not the janome.
So in conclusion I think it must be the machine.. I don't think I am of much help except that I have heard that said about the Janome. Good Luck, it is very frustrating.