Abstract: A two-stroke internal combustion engine comprising an engine block, a plurality of crankcases and including a mounting surface having therein a plurality of inlet openings each communicating with a respective one of the crankcases, a throttle housing defining a throttle passage and including a plenum mounting surface, a throttle valve in the throttle passage, and a plenum member which is separable from both the engine block and the throttle housing and which defines a plurality of intake passages each having an outlet end communicating with a respective one of the inlet openings and each having an inlet end communicating with the throttle passage such that the intake of the engine can be tuned solely by modifying the configuration of the plenum member.