Two stroke engine (10) including an engine cylinder (18) a piston (20) sliding in the engine cylinder (18) an air pump (9) a main pipe (32) connected to the air pump (9) that communicates with the engine cylinder (18) through a plurality of scavenging pipes (28) opening into the cylinder immediately above the piston (20) in its bottom dead center position an exhaust pipe also opening into the cylinder (18) immediately above the piston (20) in its bottom dead center position an auxiliary pipe (29) branching from the main pipe (32) and opening into the cylinder (18) at a level higher than the scavenging pipes (28) and exhaust pipes (33) and a valve (30) capable of selectively opening and closing the auxiliary pipe (29) and configured to supercharge and decompress the cylinder (18) during the engine start up phase.
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