Preheat oven to 325°. Mash pre-cooked sweet potatoes (skinless).
Combine flour, sugar, baking soda, cinnamon and salt in a large bowl. Mix well. Add 3/4 of the walnuts and mix to combine. In a medium bowl, mix eggs, melted butter and sweet potatoes. Add to the flour mixture and stir until just blended. Pour batter into a large 9x5 inch loaf pan and sprinkle top with remaining chopped walnuts. Bake at 325° for 45-55 minutes, or until a toothpick inserted in the center comes out clean. Cool for about 10 minutes. Remove loaf from pan and let it cool before slicing.