I have a 1600 P and I teach MQ 101 on it and have quilted over 100 quilts on it, and the only threads I seem to have problems with are sulky and connecting threads. I almost always use king tut, coats and Clark quilting thread, and mettler. I use a Organ 90/14 most of the time. If the thread is old it will break. I hold the thread up to the light and some have small burrs every so often and when you pull slightly on each end, that is where they break. Also, make sure you loosen your pressure foot tension, as that can also cause problems. I really love my machine, and I have a lot of different brands. It is a work horse. So sorry for your issues. Also, overlock thread is a thread that is very thin, that is why they use it with 3 or more cones with it on a serger. Not recommended, especially for a machine that runs at such high speeds. Also, if you are free motion quilting , don't quilt faster then your machine is sewing. Adjust your speed control.