What brand and size of thread are you using? What type and size of needle? It could be a mismatch between the thread and needle. According to Superior Threads, FMQ is best done with a fairly large topstitching needle. Superior has different recommendations for a domestic machine and longarm machine. If I can find their educational article on this topic, I will post a link here.
OK. Here's their article on needles:
http://www.superiorthreads.com/educa...e-right-needle
They have many other articles that may relate to your problem too.