Two-stroke motor

A two-stroke motor comprising a case defining a generally cylindrical upper cavity and a lower cavity, a piston slidably mounted in said upper cavity, a crankshaft disposed in said lower cavity, means connecting said crankshaft to said piston, carburetted gas supply means for supplying carburetted gas, non-carburetted gas supply means for supplying non-carburetted gas, at least one of said gas supply means including said lower cavity, and transfer conduit means for transferring gas from said lower cavity to said upper cavity, said lower cavity providing crankcase compressor means for compressing the gas supplied, said upper cavity presenting an exhaust port by which burnt gas is exhausted, said exhaust port having an upper edge, a first set of intake ports spaced apart angularly around said upper cavity and through which said non-carburetted gas supply means communicates with said upper cavity and a second set of intake ports spaced apart angularly around said upper cavity and through which said carburetted gas supply means communicates with said upper cavity, the intake ports of said first set presenting upper edges disposed below said upper edge of said exhaust port, and one of said sets of intake ports being disposed above the other set, said gas supply means being arranged to commence supplying non-carburetted gas to scavenge said upper cavity after said exhaust port is uncovered by said piston and before supplying carburetted gas to said upper cavity.