A two cycle engine having a block defining an exhaust port and a cylinder, a head, and a piston defining a combustion chamber is disclosed. The exhaust port has a resonant frequency that causes a portion of the combusted and uncombusted exhaust gasses to flow from the exhaust system and back into the combustion chamber. At a speed above the predetermined speed, a majority of the portion of the combusted and uncombusted exhaust gasses flows from the exhaust system and back into the combustion chamber without engaging the skirt of the piston.

A two cycle engine having a block defining an exhaust port and a cylinder, a head, and a piston defining a combustion chamber is disclosed. The exhaust port has a resonant frequency that causes a portion of the combusted and uncombusted exhaust gasses to flow from the exhaust system and back into the combustion chamber. At a speed above the predetermined speed, a majority of the portion of the combusted and uncombusted exhaust gasses flows from the exhaust system and back into the combustion chamber without engaging the skirt of the piston.

A method for cleaning an exhaust valve of a two-stroke internal combustion engine is provided. The method comprises: requesting an exhaust valve cleaning cycle if at least one of a first condition or a second condition is satisfied; initiating the exhaust valve cleaning cycle if at least one of a third condition or a fourth condition is satisfied; and aborting the exhaust valve cleaning cycle if at least one of the at least one of the third or fourth conditions is no longer satisfied. The first condition is a time elapsed since a previous cleaning cycle has been completed being greater than a predetermined time. The second condition is a rate of opening of the exhaust valve being less than predetermined rate. The third condition is a throttle valve being closed. The fourth condition is an engine speed being less than a predetermined engine speed.

A method for cleaning an exhaust valve of a two-stroke internal combustion engine is provided. The method comprises: requesting an exhaust valve cleaning cycle if at least one of a first condition or a second condition is satisfied; initiating the exhaust valve cleaning cycle if at least one of a third condition or a fourth condition is satisfied; and aborting the exhaust valve cleaning cycle if at least one of the at least one of the third or fourth conditions is no longer satisfied. The first condition is a time elapsed since a previous cleaning cycle has been completed being greater than a predetermined time. The second condition is a rate of opening of the exhaust valve being less than predetermined rate. The third condition is a throttle valve being closed. The fourth condition is an engine speed being less than a predetermined engine speed.

An exhaust valve assembly for a two-stroke internal combustion engine has a valve actuator, and a two-part valve having a primary and secondary valves defining first and second decompression passages respectively. The primary valve is operatively connected to the valve actuator. The primary valve is in first, second and third primary valve positions when the valve actuator is in first, second and third actuator positions respectively. The secondary valve is in a first secondary valve position when the valve actuator is in the first or the second actuator position and in a second secondary valve position when the valve actuator is in the third actuator position. The first and second valve decompression passages fluidly communicate with each other when the valve actuator is in the second actuator position, and are fluidly separate from each other when the valve actuator is the first or the third actuator position.

An exhaust valve assembly for a two-stroke internal combustion engine has a valve actuator, and a two-part valve having a primary and secondary valves defining first and second decompression passages respectively. The primary valve is operatively connected to the valve actuator. The primary valve is in first, second and third primary valve positions when the valve actuator is in first, second and third actuator positions respectively. The secondary valve is in a first secondary valve position when the valve actuator is in the first or the second actuator position and in a second secondary valve position when the valve actuator is in the third actuator position. The first and second valve decompression passages fluidly communicate with each other when the valve actuator is in the second actuator position, and are fluidly separate from each other when the valve actuator is the first or the third actuator position.

To improve the effect of preventing contamination of an element in an air cleaner. An air cleaner includes a first inlet (60) through which air is fed to an intake system air passage and a second inlet (62) through which air is fed to an intake system air-fuel mixture passage. An extended passage (72) leads to the second inlet (62), for example. A passage forming member (70, 204) forming the extended passage (72) is shaped to surround a periphery of the first inlet (60). The passage forming member (70, 204) forms a blown-back fuel diffusion preventing region (74) leading to the first inlet (60).

To improve the effect of preventing contamination of an element in an air cleaner. An air cleaner includes a first inlet (60) through which air is fed to an intake system air passage and a second inlet (62) through which air is fed to an intake system air-fuel mixture passage. An extended passage (72) leads to the second inlet (62), for example. A passage forming member (70, 204) forming the extended passage (72) is shaped to surround a periphery of the first inlet (60). The passage forming member (70, 204) forms a blown-back fuel diffusion preventing region (74) leading to the first inlet (60).

Cooperatively shaped piston and cylinder head arrangements for internal combustion engines are disclosed. The piston may have a domed head with one or more curved exhaust channels and inlet channels formed therein. The piston cylinder may have curved surfaces that are exact or close inverse or negative counterparts to the curved surfaces of all or part of the domed head, including the exhaust channels, and/or inlet channels formed on the piston.

A two-stroke internal combustion engine includes a diversion fin and an allowance slot. The diversion fin is a structure that has flanges at two ends and a rectangular longitudinal cross section profile. The diversion fin is clamped by a cylinder head and a cylinder block. The diversion fin extends along the diameter direction of the cylinder head and is positioned between an air inlet channel and an air exhaust channel. The diversion fin separates the air inlet channel from the air exhaust channel. The upper end of the diversion fin is provided with a transverse through groove at a position corresponding to an oil nozzle of an oil injector. The allowance slot is disposed on a piston and is positioned in the center of a combustor. The position of the allowance slot corresponds to the position of the diversion fin.