Pierce sweet potatoes with a fork. Bake at 400 degrees for 50 to 55 minutes or until tender. Cool slightly. Remove pulp from potatoes, keeping the skins intact. In a bowl combine the pulp with pineapple, orange juice, butter, and salt. Refill potato shells and place in a greased 13x9x2-inch baking dish. Bake at 400 degrees for 20 minutes or untill heated through.