A carburetor achieves better emission characteristics while improving a combustion state by increasing a delivery ratio of a stratified scavenging engine and reducing intake resistance. No dividing wall is provided between a throttle valve 204 and a choke valve 242, and a gap 244 between the valves 204 and 242 is opened. Intake air in both of an upper region and a lower region of the choke valve 242 flows into an air-fuel mixture passage 246 in a lower region of the fully-open throttle valve 204. A main nozzle 202 is arranged so as to be inclined toward the throttle valve 204.

To balance a low-temperature scavenging effect and a high-temperature scavenging effect. A scavenging system applicable to a leading-air type two-stroke air-cooled engine has a low-temperature scavenging passage and a high-temperature scavenging passage. The low-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. The high-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. An air is filled through a piston groove into the passages. The low-temperature scavenging passage has a relatively small capacity. The high-temperature scavenging passage has a relatively large capacity.

To balance a low-temperature scavenging effect and a high-temperature scavenging effect. A scavenging system applicable to a leading-air type two-stroke air-cooled engine has a low-temperature scavenging passage and a high-temperature scavenging passage. The low-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. The high-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. An air is filled through a piston groove into the passages. The low-temperature scavenging passage has a relatively small capacity. The high-temperature scavenging passage has a relatively large capacity.

To allow an intake negative pressure to directly act on a fuel outlet formed on a nozzle tube, and to guide a fuel discharged from the fuel outlet in the nozzle tube to the fuel-air mixture passage. A rotary carburetor (200) has a guide plate member (42) downstream of a fuel outlet (30) located in a through-hole (14). The guide plate member (42) has both side edges (42b) away from an inner wall surface (14a) of the through-hole (14). The through-hole (14) is divided by the guide plate member (42) into a first passage portion (44) and a second passage portion (46). The first passage portion (44) communicates through a piston groove with a scavenging passage of a cylinder. The fuel discharged from the fuel outlet (30) is guided by the guide plate member (42) to the second passage portion (46) and is supplied through the second passage portion (46) to a fuel-air mixture passage (24) of an engine intake system.

To allow an intake negative pressure to directly act on a fuel outlet formed on a nozzle tube, and to guide a fuel discharged from the fuel outlet in the nozzle tube to the fuel-air mixture passage. A rotary carburetor (200) has a guide plate member (42) downstream of a fuel outlet (30) located in a through-hole (14). The guide plate member (42) has both side edges (42b) away from an inner wall surface (14a) of the through-hole (14). The through-hole (14) is divided by the guide plate member (42) into a first passage portion (44) and a second passage portion (46). The first passage portion (44) communicates through a piston groove with a scavenging passage of a cylinder. The fuel discharged from the fuel outlet (30) is guided by the guide plate member (42) to the second passage portion (46) and is supplied through the second passage portion (46) to a fuel-air mixture passage (24) of an engine intake system.

A suction tube unit connected between a cylinder block and a carburetor in a stratified scavenging engine has a suction tube for mixture made of an elastic material; and a suction tube for stratified scavenging air made of an elastic material. The suction tube for mixture and the suction tube for air have, at respective inlet ends connected to the carburetor, respective wall portions which face each other and have complementary shapes. A clearance space is provided between the wall portions of the suction tube for mixture and the suction tube for air.

A suction tube unit connected between a cylinder block and a carburetor in a stratified scavenging engine has a suction tube for mixture made of an elastic material; and a suction tube for stratified scavenging air made of an elastic material. The suction tube for mixture and the suction tube for air have, at respective inlet ends connected to the carburetor, respective wall portions which face each other and have complementary shapes. A clearance space is provided between the wall portions of the suction tube for mixture and the suction tube for air.

A carburetor for a two-stroke internal combustion engine whereby airtightness is maintained and intake of uncombusted fuel into an air path is prevented. The carburetor includes a circular cylindrical valve hole and a rotary valve fitted into the valve hole such that it can rotate and is disposed perpendicularly across a fuel intake path and an air intake path which are formed substantially parallel with respect to each other, and a fuel supply-side bore which controls the flow rate along the fuel intake path and the air supply-side bore which controls the air capacity along the air path pass through part of the cylindrical portion perpendicularly to the axial direction of the rotary valve, and annular recesses formed in part of a circumferential wall of an outer circumference of the rotary valve so as not to correspond to at least the fuel supply-side bore and the air supply-side bore.

A carburetor for a two-stroke internal combustion engine whereby airtightness is maintained and intake of uncombusted fuel into an air path is prevented. The carburetor includes a circular cylindrical valve hole and a rotary valve fitted into the valve hole such that it can rotate and is disposed perpendicularly across a fuel intake path and an air intake path which are formed substantially parallel with respect to each other, and a fuel supply-side bore which controls the flow rate along the fuel intake path and the air supply-side bore which controls the air capacity along the air path pass through part of the cylindrical portion perpendicularly to the axial direction of the rotary valve, and annular recesses formed in part of a circumferential wall of an outer circumference of the rotary valve so as not to correspond to at least the fuel supply-side bore and the air supply-side bore.

A two-stroke engine includes: an intake passage that opens out to a crank chamber; a first one-way valve provided in the intake passage and permits a flow of fluid toward the crank chamber; a scavenging port having an upstream end communicating with the crank chamber and a downstream end that opens out in a wall defining a side portion of a cylinder, wherein the downstream end communicates with a combustion chamber defined above the piston at least when the piston is at a bottom dead center, and communicates with a part of the cylinder below the piston at least when the piston is at a top dead center; and an air supply passage that communicates a part of the intake passage which is located downstream of the first one-way valve with an upstream portion of the scavenging port so as to supply air to the scavenging port during air intake.