There are three general types of two cycle induction. The most simple type of air intake induction is called a piston port engine.
This type of two stroke engine has holes cut through the cylinder walls in specific areas. The second type of induction, and the most popular type, is reed block induction. This consists of multiple reed petals that allow air into the crankcase and keep it trapped there. The third type of two stroke induction is generally used in rotax two cylinder engines is the rotary valve engine. It does slightly better than reed engine because there is no restriction from reed petals. The rotary valve rotates past the crankcase intake port at a specific time to allow air through then seal the air into the crankcase.
All 2 stroke engines use their crankcase similar to a supercharger to pack more air into the combustion chamber. First the engine draws air into the crankcase through whatever induction style they have. Then as the piston travels downward the air becomes pressurized and travels through air passages called transfer ports. These ports deliver fresh air to the upper part of the cylinder. Unfortunately the exhaust port is also open which leads to some fuel escaping out of the exhaust port. This is the real reason non direct injection two stroke engines smoke and have poor emissions. Direct injection two strokes wait until the piston is above the exhaust port to inject fuel so none is lost.


