are you using the same thread in the top & the bobbin? your problem is a tension issue- perhaps start with re-threading completely from the spool - take the bobbin out & re-insert- making sure it is in correctly- then slowly start adjusting your top tension to get it even with your bobbin tension- you may need to tighten your bobbin tension too- and---do you have a new needle in? are you lowering your foot- sometimes when using the darning foot it's easy to forget to lower it-since it rides above the fabric- that can really cause a mess-