First, double check that your foot is installed correctly. They can be tricky! Next make a small sandwich, like 6" square and sew to make sure the foot is working.
Having said that, a walking foot is not powerful enough to pull a whole quilt thru your machine. You have to give it lots of help. There should be no drag on the quilt in any direction. The quilt needs to be supported front, back, and left. Extra tables are a great start. If you google 'youtube king size quilt domestic machine', there are lots of videos with suggestions.