Try lowering your tension to 3. 5 is pretty high.

I have a simple janome and it needs to be cleaned. it has the same problem I would clean it out also. I am trying to get this one quilt finished before I take mine in to be serviced.

I think most machines have a stitch length of 2.5 as the default setting? Try increasing the stitch lenght...I only use 1.5 when I am paper piecing because the shorter stitch makes it easier to remove the paper.