Exhaust and Intake:

At 82° ATDC, along with the piston near the end of its power stroke, the exhaust cam starts to lift the exhaust valves follower. A valve lash is taken up, and 9° later (91° ATDC), a rocker arm forces the exhaust valve off its seat. The exhaust gasses begin to escape within the exhaust manifold, as display in below figure. Cylinder pressure begins to decrease.

After the piston travels three-quarters of its (down) stroke, or 132° ATDC of crankshaft rotation, the piston begins to uncover the inlet ports. As the exhaust valve is still open, an uncovering of the inlet ports lets the compressed fresh air enter the cylinder and helps cool the cylinder and scavenge the cylinder of the remaining exhaust gasses. Generally, exhaust and intake occur over around 96° of crankshaft rotation. At 43° ABDC, a camshaft starts to close the exhaust valve. At 53° ABDC (117° BTDC), a camshaft has rotated enough to permit the spring pressure to close the exhaust valve. In addition, as the piston travels past 48°ABDC (5° after the exhaust valve begins closing), the intake ports are closed off through the piston.

Figure: 2-Stroke Exhaust               Figure: 2-Stroke Intake