In tension issues you will have to find by trial and error what works best to FMQ on your machine and on the quilt sandwich you are doing. On my machine I return to the factory suggested tension for regular sewing and then start changing the tension a bit at a time. Make sure if you have a thread spool with the little cut in it for the thread end, that it is not catching. Inspect the thread's path and make sure it is clean and clear. Make sure you have the zig zag sole plate on your machine so that the push/pull of the needle doesn't make it hit the sole plate and clip the thread. Make sure your needle hasn't slipped down in the holder a smidge.