I have a 6600 also and I will say that it has the most tempermental tension of any machine I have ever sewn on! I have had the same issues but I'm just starting to learn FMQ so I thought it was just me! good luck

Take it back to the dealer. Even if is is something you are doing, they can help you sort through your techniques, and guide you through steps in using the machine so that you will have a more pleasant experience. People who sell these name brand machines usually provide instruction for the asking. They also usually offer classes covering all of the functions.

Never had this issue with my Janome 6600. What thread are you using? I cannot FMQ though I can do Piecing with Coats & Clarks all purpose from WalMart.
My tension is 7 pressure 1, feed dogs down, Mode 2, D01. Think long as it is a straight stitch it doesn't matter.

Clean the lint out, even under the bobbin case and up above the needle. See if thread stuck in tension wires above the needle.

Hope it gets better. I never had the problem you experienced but in learning FMQ I have my share of eyelashes on the bottom etc.. Good luck

Hope it is getting better for you...if not, I would go to your dealer and see if they can help you with the problem...and/or sign up and take a class somewhere...once you have the hang of it, you probably will be doing some beautiful quilting!

Take it back to the dealer. It's should be HIS/HER problem. Had similar trouble with a serger. After four trips, I told him with a customer listening, that he could keep it, and that I got a lemon. He gave me a new machine--no more problems.

Sandy

Have you tried pulling your bobbin thread up to the top before you start stitching; I do this and it helps alot.

Leah Day, of the Free Motion Quilting project blog, recommends doing fmq with the feed dogs up because dropping them can cause tension problems on some machines. Check out her blog - really neat!!

Leah Day (who is the machine quilting "guru" for some of us) never lowers her feed dogs for that very reason - the tension will get all messed up. I've tried it her way, and I have say it does make a huge difference! So good luck with your machine and I hope it continues to do well for you.

Edited to Add: Hey krisgray, we are sharing a brain!

So glad you got that taken care of. This is one of the many ways this quilting forum helps. So many wonderful, helpful friends. :)

Again someone's problem brings new knowledge to the table. I read all the comments and having the feed dogs up was wow new to me. I will have to try it next time. You guys are such problem solvers and enlighteners for so many.