A spark-ignition reciprocating piston engine has at least one piston cylinder, at least one inlet port arranged at an end of the cylinder, an inlet valve located at the inlet port and that is movable to open and close the inlet port, and an inlet conduit leading to the inlet port for feeding a fluid from a fuel feed to an inlet area of the inlet port. The engine includes a partition arranged within the inlet conduit which divides the inlet conduit into at least two partial conduits over at least a portion of a length of the inlet conduit between the fuel feed and the inlet area. At least one of the partial conduits is connected to the fuel feed. The partial conduits converge directly in front of the inlet port to form the inlet area. The partition is located within a plane that extends essentially transversely to an axis of the cylinder at least in the inlet area. The partition has an end edge facing the inlet area, and has at least one portion that is movable to deflect a flow of the fluid on blow-by from the inlet conduit, through the inlet port, and into the cylinder. A controllable actuation arrangement is connected to the portion for changing a distance from the end edge to the inlet port.