A powered fastener driver comprising: a first cylinder; a first piston positioned within the first cylinder, the first piston being moveable between a top-dead-center, TDC, position and at or near a bottom-dead-center, BDC, position; a second cylinder in fluid communication with the first cylinder; a second piston positioned within the second cylinder, the second piston being moveable between a top-dead-center position and a bottom-dead-center position to initiate a fastener driving cycle; a drive blade coupled to the second piston for movement therewith; and a drive mechanism configured to drive the first piston between the top-dead-center position and at or near the bottom-dead-center position to complete the fastener driving cycle; characterized in that the powered fastener driver further comprises a back-pressure adjustment mechanism in communication with the second cylinder, the back-pressure adjustment mechanism configured to adjust a volumetric flow rate of air exhausted from the second cylinder by the second piston during the fastener driving cycle, wherein the back-pressure adjustment mechanism includes a basket rotatably supported within a housing of the powered fastener driver, and wherein the basket includes an opening that is selectively aligned with a window formed in the housing to adjust an effective size of the window, and therefore the volumetric flow rate of air exhausted from the second cylinder by the second piston during the fastener driving cycle and, further comprising a check door that is movable between an open position, in which a second window in the housing is opened to permit atmospheric air to enter the second cylinder via the basket in response to the second piston moving from the bottom-dead-center position toward the top-dead-center position, and a closed position, in which the second window is closed and atmospheric air is prevented from exiting the second cylinder via the basket in response to the second piston moving from the top-dead-center position toward the bottom-dead-center position. a first cylinder; a first piston positioned within the first cylinder, the first piston being moveable between a top-dead-center, TDC, position and at or near a bottom-dead-center, BDC, position; a second cylinder in fluid communication with the first cylinder; a second piston positioned within the second cylinder, the second piston being moveable between a top-dead-center position and a bottom-dead-center position to initiate a fastener driving cycle; a drive blade coupled to the second piston for movement therewith; and a drive mechanism configured to drive the first piston between the top-dead-center position and at or near the bottom-dead-center position to complete the fastener driving cycle; characterized in that the powered fastener driver further comprises a back-pressure adjustment mechanism in communication with the second cylinder, the back-pressure adjustment mechanism configured to adjust a volumetric flow rate of air exhausted from the second cylinder by the second piston during the fastener driving cycle, wherein the back-pressure adjustment mechanism includes a basket rotatably supported within a housing of the powered fastener driver, and wherein the basket includes an opening that is selectively aligned with a window formed in the housing to adjust an effective size of the window, and therefore the volumetric flow rate of air exhausted from the second cylinder by the second piston during the fastener driving cycle and, further comprising a check door that is movable between an open position, in which a second window in the housing is opened to permit atmospheric air to enter the second cylinder via the basket in response to the second piston moving from the bottom-dead-center position toward the top-dead-center position, and a closed position, in which the second window is closed and atmospheric air is prevented from exiting the second cylinder via the basket in response to the second piston moving from the top-dead-center position toward the bottom-dead-center position.