your bobbin thread needs to be tightened, look in your book.
titanium needles are best, not all metallic thread is good. if it is not smooth as you slide through your finger tips, get rid if it. if it twist and turns into knots as you take it off the cone, get rid of it.life is to short to let this get the best of you. fine a better thread. yli, iscord, is better.