I have a PQ1500s that I adore ! For FMQ I drop my dogs all the way down, and set my stitch length to roughly 2 and 1/4 ( about 1 " click " past the 2 ). I know everyone will tell you that mechanically stitch length has nothing to do with your stitches once your feed dogs are lowered, but all be danged on THIS machine it does LOL. Also make sure you raise your presser foot pressure dial alllll the way up to the top to give you the least resistance.
Also, you might need to purchase a new FMQ foot. I purchased my machine and it came with one, but it does NOT fit properly ! You want to get a Juki Free Motion Quilting Foot. They have one here so you can see what I am talking about.
http://www.kenssewingcenter.com/juki...t-p-28478.html This foot works and behaves beautifully on the PQ1500.