A spout assembly and related method of regulating the flow of particulate material. The spout assembly includes a chute, at least first and second plates, and a counterbalance mechanism. The first and second plates are positioned downstream from the chute, the lower ends of the first and second plates defining an opening with an area that is smaller than a cross-sectional area of the chute so that the material may accumulate prior to passing through the opening. The counterbalance mechanism produces a biasing force on the first and second plates toward the centerline to adjust the area of the opening, and permits the first and second plates to move outwardly away from the centerline in response to the weight of the accumulated material. The counterbalance mechanism includes at least a first separately adjustable counterbalance coupled to the first plate and a second separately adjustable counterbalance coupled to a second plate.