INTAKE STROKE: The piston goesdown, creating a vacuum in the cylinder
which draws gas through open intake valve into the space above the
piston.

COMPRESSION STROKE: The piston comes up with both valves closed,
highly compressing the gas into the space left between thetop of the
piston and cylinder head.

POWER STROKE: At this point the magneto sends high tension current to
the spark plug, firing or exploding the compressed gas and driving the
piston down.

EXHAUST STROKE: Exhaust valve opens and theupward stroke of the piston
forces out all of the burnt gases, thus completing the power cycle.