Sounds like you're on your way to more quilting. Wall quilts need as much quilting as ones that are washed because as they hang, if quilted insufficiently, the batting, top and back start to sag and the quilt looks "old" quickly. I think you indicated that the machine is having no trouble with FMQ when using colored thread- so that covers that question. So it's on to the monofilament thread. It needs a looser tension than cotton or poly thread because its stiffer and a little sticky going through the machine. Due to it's size a 65-70 microtex needle is recommended. Also, older monofilament thread was definitely breaking more often. Get a new spool of poly that is a good brand: YLI, Superior etc. Monofilament has some benefits and in some situations, such as outlining motif or applique, it is the thread of choice.