Here is a link about pairing needles to thread -- for 50wt thread you should use the 14 needle (I use top stitch needles for most of my sewing) for quilting -- you can get away with a 12 for piecing.
http://www.quiltingboard.com/resources/article-61.html
That said, my machine hates Sulky thread -- I can use anything else. You also might try a different needle -- I had issues and an entire box of new needles must have had burrs since when I went to a different box of needles I had no problems.