I'm going to interrupt here for a second to explain how that fresh mixture is prevented from being expelled. Unfortunately, some of the fresh fuel mixture is usually expelled as well. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder.
Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. The fuel mixture is then compressed in the crankcase during the remainder of the stroke. During the downward stroke the poppet valve is forced closed by the increased crankcase pressure. The illustrated engine features a poppet intake valve, however many engines use a rotary value incorporated into the crankshaft. Intake, The fuel/air mixture is first drawn into the crankcase by the vacuum created during the upward stroke of the piston. 2 is the fact that they have fewer moving parts, which decreases the constant load on the engine, allowing it to burn the air-fuel mixture more efficiently, and reach much higher revolutions per minute. 1 is the displacement, they generally have smaller combustion chambers, which means less fuel burned. Two stroke motors are more efficient that four strokes for a few reasons. Here is an overview of how two stroke motors work.
