It doesn't take much of a burr to cause a lot of problems. I had a small burr on the top of my bobbin and I went a bit crazy until finding it.
Also, I like the embroidery needles...they have a longer eye so that the thread doesn't wear while stitching.
I only use Polyester embroidery threads...they seem to be a bit stronger than rayon. Don't just stick to the Brother threads...they don't work well for me. But they work great for others.