The old sewing machine guy will solve it. Does it stitch through the fabric when not threaded? I'm thinking something might hinder the needle punch power, which usually is cleaning, oiling, and wiping off the motor belt and groove in motor pulley and hand wheel. The Featherweight is known to mishave if there's thread caught under the base, and it's a bit cumbersome to check and clean it out thoroughly.
This is a good tutorial on it.