Grease eighteen 2-1/2-inch muffin cups or line the muffin cups with paper baking cups and set aside.
In a medium mixing bowl, combine flour, sugar, cinnamon, baking soda, mace, salt, baking powder, nutmeg, and cloves. Make a well in the center of the flour mixture and set aside.
In another bowl, combine the eggs, pumpkin, and melted butter or margarine. Add the pumpkin mixture all at once to the flour mixture. Stir until just moistened (batter should be lumpy). Fold in the chocolate pieces.
Spoon the batter into prepared muffin cups, filling each two-thirds full. Bake in a 350 degree F oven for 20 to 25 minutes or until a wooden toothpick inserted into the centers of the muffins comes out clean. Don'toverbake. Remove from muffin cups, serve warm.