On my Singers, I have to make sure that when I pull the thread end around the side of the needle, the thread goes underneath the little piece of metal that goes through the eye of the needle. If I do that, and wrap the thread around towards the back of the needle, it threads perfectly every time. It took me a while to figure out I wasn't always going underneath that metal piece, and it wouldn't thread properly :roll:
When I attach my walking foot, I put it in from the back, and it seems to fit in easier, and the threader does not get in the way.