I had a similar problem and after rethreading, changing needles for size and type I discovered that the foot to my FMQ foot was loose. I have a Janome 8900 which has three interchangeable feet to FMQ (open toe, closed toe and round plastic). The screw that holds that part of the foot on had become loose and I didn't notice it and it allowed enough give in the stitching to break the thread. I also adjusted the pressure of the foot against the fabric to be a little more so the fabric stayed closer to the bed of the machine. Between those two I was up and running.
If you have a speed control on your machine I found it helpful to find your "sweet spot" speed wise and then all you have to worry about is regulating the speed with which you move your hands since you can just push down on the foot pedal without having to control the speed of the needle.