In one of my serger books it suggests confirming the needles are fully inserted in the needle clamp. Replace your needles making sure you have the correct ones - making sure the eye is to the front and the scarf to the back, make sure the presser foot is lowered as some sergers can't form stitches with the foot up, it could be the thread - tighten the tensions slightly. Try all of these and see if that might be the problem. Maybe your timing is off. The book I have is called the Ultimate Serger Answer Gude by Naomi Baker, Gail Brown and Cindy Kacynski - if nothing else perhaps your local library can get you a copy to look at. Just a suggestion. Budster