Abstract: A carburettor includes a primary air passage (19), an adjustable throttle valve (8) situated within the primary air passage, a fuel supply nozzle (28) communicating with the primary air passage and connected to a fuel metering valve for varying the amount of fuel discharged through the nozzle. The fuel metering valve includes an elongate sleeve (32) movably accommodating an elongate valve member (33). The sleeve and valve member define a fuel inlet space (35). A fuel inlet (37) communicates with the fuel inlet space. A fuel outlet (39) passes through the wall of the sleeve (32) and communicates with the fuel supply nozzle (28). A portion of the outer surface of the valve member (33) is so profiled that the valve member (33) is movable relative to the sleeve (32) such that the area of communication between the fuel inlet space (35) and the outlet (39) varies progressively between a maximum and a minimum value.

Abstract: A carburettor including a primary air passage, an adjustable throttle valve situated within the primary air passage, a fuel supply nozzle communicating with the primary air passage and connected to a fuel metering valve for varying the amount of fuel discharged through the nozzle and a rotary input shaft adapted to be connected to an engine speed control member and which is connected to the throttle valve to move the throttle valve between open and closed positions. The rotary input shaft is also connected to a carriage to move the carriage, the carriage carrying at least one elongate inclined ramp which extends in the direction of movement of the carriage and which is engaged by a follower connected to the valve member. Rotation of the input shaft results in movement of the throttle valve and in movement of the carriage and thus of the elongate ramp, wherein the follower is moved transverse to the length of the ramp and the valve member of the fuel metering valve is thus also moved.

Abstract: A carburettor including a primary air passage, an adjustable throttle valve situated within the primary air passage, a fuel supply nozzle communicating with the primary air passage and connected to a fuel metering valve for varying the amount of fuel discharged through the nozzle and a rotary input shaft adapted to be connected to an engine speed control member and which is connected to the throttle valve to move the throttle valve between open and closed positions. The rotary input shaft is also connected to a carriage to move the carriage, the carriage carrying at least one elongate inclined ramp which extends in the direction of movement of the carriage and which is engaged by a follower connected to the valve member. Rotation of the input shaft results in movement of the throttle valve and in movement of the carriage and thus of the elongate ramp, wherein the follower is moved transverse to the length of the ramp and the valve member of the fuel metering valve is thus also moved.

Abstract: The carburetor (1) includes a flow duct including rich (60) and lean (50) flow passage in parallel, through which, in use, air flows in a flow direction and which are separated by a substantially planar partition (30), at least one fuel jet 5 communicating with the rich passage (60), the partition (30) including an aperture (40) towards which the fuel jet (5) is directed, and a substantially planar butterfly valve (20) being received in the aperture (40) so as to be pivotable between a first position, in which the flow duct is substantially closed and the aperture (40) is substantially open, and a second position, in which the flow duct is substantially open and the aperture (40) is substantially closed, the upstream half of the aperture (40) being defined by an upstream semi-annular seating ledge (48) affording an upstream seating surface which is engaged by one of the surfaces of the butterfly valve (20) when it is in the second position and a first end surface which extends between the upstream seating sur

Abstract: A carburettor includes a primary air passage (19), an adjustable throttle valve (8) situated within the primary air passage, a fuel supply nozzle (28) communicating with the primary air passage and connected to a fuel metering valve for varying the amount of fuel discharged through the nozzle. The fuel metering valve comprises an elongate sleeve (32) movably accommodating an elongate valve member (33). The sleeve and valve member define a fuel inlet space (35). A fuel inlet (37) communicates with the fuel inlet space. A fuel outlet (39) passes through the wall of the sleeve (32) and communicates with the fuel supply nozzle (28). A portion of the outer surface of the valve member (33) is so profiled that the valve member (33) is movable relative to the sleeve (32) such that the area of communication between the fuel inlet space (35) and the outlet (39) varies progressively between a maximum and a minimum value.

Abstract: A carburettor for a two-stroke engine includes a substantially circular section flow duct comprising rich (42) and lean (44) flow passages in parallel, through which, in use, air flows in a flow direction and which are separated by a substantially planar partition (66). At least one fuel jet (60, 61, 62) communicates with the rich passage (42) and the partition (66) includes an aperture (68) towards which the fuel jet is directed. A substantially planar butterfly valve (20) is received in the aperture (68) so as to be pivotable between a first position, in which the flow duct is substantially closed, and a second position, in which the flow duct is substantially open. The butterfly valve (20) is carried by a pivotal shaft (2) mounted to pivot about an axis which extends through the flow duct substantially diametrically.

Abstract: The carburettor (1) includes a flow duct comprising rich (60) and lean (50) flow passages in parallel, through which, in use, air flows in a flow direction and which are separated by a substantially planar partition (30), at least one fuel jet 5 communicating with the rich passage (60), the partition (30) including an aperture (40) towards which the fuel jet (5) is directed, and a substantially planar butterfly valve (20) being received in the aperture (40) so as to be pivotable between a first position, in which the flow duct is substantially closed and the aperture (40) is substantially open, and a second position, in which the flow duct is substantially open and the aperture (40) is substantially closed, the upstream half of the aperture (40) being defined by an upstream semi-annular seating ledge (48) affording an upstream seating surface which is engaged by one of the surfaces of the butterfly valve (20) when it is in the second position and a first end surface which extends between the upstream seating

Abstract: A carburettor for a two stroke engine includes a flow duct including rich and lean flow passages (160, 150) in parallel, through which, in use, air flows in a flow direction and which are separated by substantially planar partition (130). At least one fuel jet (5) communicates with the rich passage (160) and the partition includes an aperture (140) towards which the fuel jet is directed. A substantially planar butterfly valve (120) is received in the aperture so as to be pivotable between a first position, in which the flow duct is substantially closed and the aperture is substantially open, and a second position, in which the flow duct is substantially open and the aperture is substantially closed.

Abstract: A carburettor is connected into the inlet duct (48) of an internal combustion engine. The inlet duct is divided by a dividing wall (64) into a rich passage (42) and a lean passage (44). The carburettor includes a fuel chamber (4) and defines a flow duct divided by a planar partition (66) into a rich duct (30) and a lean duct (32) which communicate with the rich and lean passages, respectively. The partition (66) defines an aperture (40) in which a planar butterfly valve (20) is pivotably mounted. A number of fuel supply orifices (61, 62) communicate with the fuel chamber (4) and with the duct (30) at a position opposite to the aperture (40).

Abstract: A reciprocating piston engine (2) includes an exhaust system comprising an exhaust pipe (8) which communicates with a silencer (10), whose upstream portion (11) is divergent in the direction of gas flow through it, an oxidising catalyst (12) and an air supply pipe (14) communicating with the exhaust pipe at a position upstream of the catalyst and silencer. The air supply pipe (14) includes a Reed valve (16) which is adapted to open under a pressure differential to permit air to flow into the exhaust pipe. In order to maximise the air flow into the exhaust pipe the effect of pressure pulses within the exhaust pipe is utilised and for this purpose 3L2−(2L1+L2) is equal to ±0.25 to 0.

Abstract: A crankcase scavenged two-stroke engine includes a piston reciprocably mounted in a cylinder. The cylinder wall has an exhaust port and a rear transfer port opposed thereto formed in it. The rear transfer port communicates with the interior of the crankcase via a rear transfer passage and is arranged to open before the exhaust port closes, whereby, in use, the cylinder is scavenged. An inlet duct is arranged to supply combustion air to the crankcase and a throttling valve is arranged to throttle the flow of air through the inlet duct. A carburettor is arranged to supply fuel into the inlet duct. The interior of the crankcase is divided into at least two separate crankcase volumes, a rich volume (V1,V2) and a lean volume (V3). Each crankcase volume communicates with the cylinder via a respective hole in the crankcase wall. The cylinder wall also has at least one lateral transfer port formed in it at a position between the rear transfer port and the exhaust port.

Abstract: A crankcase scavenged two-stroke engine includes a piston reciprocably mounted in a cylinder. The cylinder wall has an exhaust port and a rear transfer port opposed thereto formed in it. The rear transfer port communicates with the interior of the crankcase via a rear transfer passage and is arranged to open before the exhaust port closes, whereby, in use, the cylinder is scavenged. An inlet duct is arranged to supply combustion air to the crankcase and a throttling valve is arranged to throttle the flow of air through the inlet duct. A carburettor is arranged to supply fuel into the inlet duct. The interior of the crankcase is divided into at least two separate crankcase volumes, a rich volume (V1, V2) and a lean volume (V3). Each crankcase volume communicates with the cylinder via a respective hole in the crankcase wall. The cylinder wall also has at least one lateral transfer port formed in it at a position between the rear transfer port and the exhaust port.