Crankcase scavenged two-stroke engines

A two-stroke engine of crankcase scavenged type including a crankcase, a cylinder, a piston reciprocably mounted in said cylinder, an exhaust port communicating with said cylinder, an inlet port arranged to supply combustion air to said crankcase, a transfer port comprising at least two transfer passages extending between said crankcase and said cylinder, said transfer port being arranged to open before said exhaust port closes whereby, in use, said cylinder is scavenged, and fuel metering means which communicates with at least one but not all of said transfer passages and is arranged to supply fuel into said one transfer passage, said fuel metering means including a metering valve and actuating means connected to said metering valve, said actuating means being arranged to modulate said metering valve in response to the mass flow rate of air through said inlet port, and fuel supply means arranged to supply pressurised fuel substantially continuously to said metering valve, non-return means being provided in said transfer passage and arranged to prevent the flow of said fuel from said one transfer passage into said crankcase.