Janome 1600P-DB Mechanical Sewing Machine

I purchased this machine on line with a Grace Quilting frame. I have had a difficult time inserting the round needles (no flat side) and difficult time finding them in stores. Finally I use a needle holder to position the needle while inserting it. Also much problems with using different threads,such as polyester. It only likes the expensive kinds like King Tut. The tension gives me a headache every time I use it. I have had to take out row after row of stitching. And I am a semi-pro and sell quilts all the time. I would not recomend this machine, it is too heavy to remove from frame to take out for repairs or use alone so what good is the knee lift?