I have the Lily 540 and the Sapphire 870 and they require different walking feet. when you attach the walking foot the moving parts should align with the feed dogs. the Lily 540 feed dogs are much narrower than the Sapphire, maybe you do have the wrong foot for your model? I did try to make-do with just the one foot but it wouldn't pull the fabrics through properly. Hope that's all that your problem is.