Preheat oven to 350°. Grease and flour a 10-in. fluted or plain tube pan., In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs, 1 at a time, beating well after each addition. Beat in lemon juice and vanilla. Add flour alternately with 7UP, beating well after each addition. , Transfer batter to prepared pan. Bake until a toothpick inserted in center comes out clean, 65-75 minutes. Cool in pan 20 minutes before removing to a wire rack to cool completely., For glaze, in a small bowl, mix confectioners' sugar, lemon juice and enough 7UP to reach desired consistency. If desired, stir in zest. Drizzle over cake.