Four cycle, two cycle

FOUR STROKE CYCLES
A four stroke does four things to complete one cycle.

INTAKE
During the intake, the crankshaft will rotate to pull to piston down, this then creates a vacuum in the cylinder while the valves opens this will then allow air to be pulled through the carbeurator while at the same time picking up fuel. to close the intake valve  , the crankshaft rotates to a low spot on the lobe to allow the valve springs to close the   intake valves.

COMPRESSION
This is when the air and fuel is being compressed, this cycle allows both intake and exhaust valves to closed.

POWER 

during the power stroke, the spark plug fires just before the piston and the crankshaft reaches (TDC), top dead centre then the fuel and air mixture is ignited. the heated gasses will then expand forcing the piston down. power is being produce in this part.

EXHAUST

The exhaust valves opens by the camshaft to allow all the burnt gasses out. this is when the piston will  be forced back up by the camshaft.

TWO STROKE