I bought a new machine a few months ago and the dealer told me not to use Coats & Clark thread.

I was using the wrong size needle for the thread I had for 2 1/2 years and complained about my sewing machine all the time. Finally I told my dealer I could only use 50 wt. Presencia cones and he took the thread I said I couldn't use and put in the right size needle and my machine just sewed perfectly fine. He said I needed a bigger needle for 40 wt. thread. So now I always make sure the thread and needle match. Makes all the difference! Use to clunk and clatter and thread would break before. Now it purrs!!

Or perhaps that is where the little quilting police hide to give us a bad time :)

If you have used canned air on that machine, it may have blown lint or thread deep INTO the workings of the machine, and that might be your problem. If you can't find it, you may have to take it in to be serviced and tell them what you did. Canned air is not recommended for sewing machines.

I have done tests with Coats and Clark on my various machines and I find it to be lower quality, based on what I've learned about threads in classes on threads. If you look at it under a microscope, you will see that C & C has all sorts of short pieces of thread sticking out over it and it is poor quality. Good quality threads have long staple cotton and do not have these short threads.