Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, 2 tablespoons pecans, baking powder, pumpkin-pie spice, and salt in a large bowl. Combine milk and next 4 ingredients (milk through eggs); add to flour mixture, stirring until smooth. Stir in sweet potatoes.
Spoon about 1/4 cup batter onto a hot nonstick griddle or large nonstick skillet. Turn pancakes when tops are covered with bubbles and edges look cooked. Sprinkle pancakes with 2 tablespoons pecans.