What is 2 stock engine?

A 2 stock engine or a two-stroke cycle engine is a type of internal combustion engine in which the piston completes two strokes or half-revolutions of the crankshaft per power cycle. During the first stroke, the fuel-air mixture is compressed and ignited, and during the second stroke, the exhaust gases are expelled from the cylinder. The two-stroke engine differs from the more commonly used four-stroke engine in that it does not have valves to control the flow of fuel and air into and out of the cylinder. Instead, it uses a piston that moves up and down the cylinder to cover and uncover ports that allow the fuel, air, and exhaust gases to enter and leave.