Sift together the flour, salt, sugar and baking powder into a large bowl. In a separate bowl combine the milk, eggs, oil, zest and juice. Add, all at once, to the flour mixture. Stir lightly with a fork just until moist, batter will be lumpy. Spoon into greased muffin cups, filling each 1/2 full. Bake at 350 degrees F for 20 - 25 minutes or until golden and they test done.