I have a new-to-me Janome 6600 and am having trouble zigzagging a quilt sandwich. The top of some of the zigzags are squared off - it even sews a few straight stitches once in a while. I'm quilting a full bed quilt when on my old machine the largest I did was twin. So size and drag are a variable. I have changed needles - using a 14-90. I've rethreaded, cleaned out -- all I know to do. I figure it's user error, but I can't figure out what I'm doing wrong. Suggestions?
I puddle the quilt and have stools to hold it's weight to the front - it's on a table so there is support to the left and behind the machine. I have the foot pressure on 2 - had in on 1 for a while. Tension is on 7 - but I've tried it on every number. I have the red dot bobbin holder in there. Using foot A, mode 2, stitch 08. I'm stitching on the piecing seams around blocks.