Power stroke is only 1 / 4 of the cycle, the piston movement during remaining cycles is ensured by the inertia of crankshaft and associated rotating parts. Two-stroke engine differs from the four-bit more complicated workflow, but its design simply due to lack of timing mechanism and its drive (in the head is just a candle). We also have a two-stroke engine and off compression stroke, but the issue of admission and are united in a special process called purging. Purge begins at the end of the stroke and ends at the beginning of the compression stroke, ie when the piston is near BDC. Fuel mixture from the carburetor comes not just in the cylinder, and first sucked into the crankcase engine under the influence of depression formed therein when the piston moves to TDC.
At this time the cylinder is compressed mixture of the previous cycle. Candle ignites the mixture, and the piston under the action of expanding gases moves down, rotating the crankshaft and a new batch of compressing the mixture in the crankcase. Before reaching the BDC, the piston opens the exhaust window in the wall of the cylinder and the exhaust gases escape through the exhaust pipe into the muffler. Cylinder pressure drops sharply. Then the piston opens the window purge and fresh mixture, compressed in the crankcase passes through the bypass ka nalam, enters the cylinder through a purge box and filling it and forcing the remaining exhaust gases. Piston BDC and is moving up, closes the first purge the window, and then the outlet box.