Jamming. I interpret this as meaning the fabrics pull down into the needlehole. Right?
When I have my jamming problem, it is because I have my zigzag needle plate installed. If I change to the single needle hole plate, the problem is solved. And like others have suggested, use a sharp needle.
WARNING!!! be sure to return to the zigzag needle plate if you are going to use a decorative stitch OR you will break a needle and bugger up your plate.
Suzanne