Preheat oven to 350°.
Coat a 10-inch tube pan with cooking spray; dust with breadcrumbs.
Lightly spoon flour into dry measuring cups, and level with a knife. Combine the flour, baking powder, and salt in a bowl, and stir well with a whisk. Beat the butter in a large bowl at medium speed of a mixer until light and fluffy. Gradually add the granulated sugar and vanilla, beating until well-blended. Add the eggs, 1 at a time, beating well after each addition. Add flour mixture to sugar mixture alternately with milk, beating at low speed, beginning and ending with the flour mixture.
Spoon two-thirds of batter (about 4 cups) into prepared pan. Add syrup and baking soda to remaining batter in bowl, stirring just until blended; spoon on top of batter.
Bake at 350° for 1 hour and 15 minutes or until cake pulls away from sides of pan. Cool in pan 10 minutes on a wire rack; remove from pan. Cool completely on wire rack. Sift cocoa over top of cake.