Preheat the oven to 325 degrees F (165 degrees C). Grease and flour a 9x13-inch pan.

Combine flour, cinnamon, baking powder, baking soda, and salt together in a large bowl; set aside.

Mix sugar, oil, and eggs together in a separate bowl. Beat in flour mixture. Stir in carrots, pineapple, coconut, and walnuts. Pour cake batter into the prepared pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 35 to 40 minutes. Allow to cool.