a bigger needle (the eye) and loosening the top tension will help with the sulky thread, if the eye is too small it frays the thread as it goes through...i like the yli varigated threads but have experienced the same problem with them it is not just sulky. also 'sewers aid' helps, it is a liquid (in a bottle that looks like fray-check...do not get them mixed up) the sewers aid is a 'thread conditioner' which helps cut down on fraying and helps the thread run smoothly through your machine (like waxing for hand sewing) sometimes it makes a difference what you are putting in your bobbin too. once you get it to work make notes about your tension settings and needle being used so you can set up the same for the next time.