Lighter, better, more efficient and cost less, that are the reasons why two-stroke engine is attracted by people. A two-stroke engine is also called two-cycle engine, it completes a power cycle in only one crankshaft revolution and with two strokes, or up and down movements.

Components
The basic components of a two-stroke engine include combustion chamber, spark plug, pistons, reed valve, crank case, exhaust outlet and cylinder block, some come with cooling fins, but most two-stroke engines are air cooled. Some two-stroke engines have a more elaborate ignition system, featuring a distributor and ignition coil. A water-cooled two-stroke engine will also have a water pump and radiator too.

In a “two stroke” engine, every second stroke is a “power stroke” (where the piston is burning gas and making power) and the other stroke is an “exhaust stroke” where the burned up gasses are cleaned from the cylinder.

So, what are the advantages?
Compact, lighter, cost less
Two-stroke engines do not have valves, simplifying their construction. Compared to 4-stroke engines, they have a greatly reduced number of moving parts, are more compact and significantly lighter. Additional, two-stroke engines are cost less to manufacture.

High power to weight ratio
Two-stroke engines often provide high power-to-weight ratio, usually in a narrow range of rotational speeds called the “power band”. Fire once every revolution which gives two-stroke engines a significant power boost. Thus, they have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

Problems of the two-stroke engine (Read more Are Two-Stroke Engines Better than Four-Stroke Engines?)
Pollute
This is the big disadvantage of two-stroke engine, each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port. And the oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.

Shorter life than four-stroke engine
They can’t live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster.
Higher Consumption
Fresh mixture is escaping with exhaust gases during exhaust stroke.

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