I learned in my FMQ boot camp, class, if your straight stitch has no tension problems, then don't mess with your tension. The culprit is the matching of needle to thread, or user error. I brought a brand new machine to class. I FMQ'd The day before the class, it was perfect. But I choose a new thread for the class and after several jams and broken needle, the instructor sat with me to see what was happening. I was doing everything right, and my Machine was threaded properly. After 10 minutes of continued issues, the instructor took my thread off the holder and turned the cone upside down, inside the cone WAS PRINTED the needle recommendation. Microtex 90/14. Luckily the shop sponsoring the boot camp had one packet of Microtex that I needed. Changed out the needle, no problems at all the remainder of the class. From that point on, I always check my stitching with straight stitch before doing FMQ. Best wishes with the Janome 6700. Great machine. Love Janomes.
The one I took to class was the 8900.