Abstract: A method of operating a two stroke cycle crankcase scavenged internal combustion engine, comprising selectively delivering exhaust gas from a location downstream of the engine exhaust port to the engine crankcase to be delivered together with air in the crankcase to the engine combustion chamber. The quantity of exhaust gas delivered to the crankcase during each engine cycle is controlled according with engine operating conditions and the rate of supply of exhaust gas to the crankcase is controlled relative to engine operating conditions such as by an ECU managed valve that responds to engine operating conditions such as load, speed and temperature. The exhaust gas is admitted to the crankcase during a period when the pressure in the crankcase is below that of the available exhaust gas.