Abstract: A lubrication system for an engine includes an oil discharge port in a lower section of a crankcase. A crankshaft, with a crank web attached thereto, rotates in a rotation direction within the crankcase. A first distance is formed between the crank web and a first inner surface of the crankcase, downstream of the oil discharge port. A second distance is formed between the crank web and a second inner surface of the crankcase, upstream of the oil discharge port. The first distance is less than the second distance. Also, the oil discharge port is defined in part by a back edge, which is wedge shaped and points in a direction opposite the rotation direction of the crankshaft. The back edge scoops oil from the crank web and into the oil discharge port.

Abstract: A crankshaft rotation structure for a four cycle engine has a radial ball bearing fitted into a first main bearing section of a crankcase and a radial roller bearing fitted into a second main bearing section of the crankcase. The crankshaft is rotatably supported by the radial ball bearing and radial roller bearing. Furthermore, an oil jet nozzle for cooling a piston is provided in the second main bearing section. The diameter of the shafts for attachment of the bearings can be made the same, even if the outer diameter of the radial roller bearing is decreased compared to the outer diameter of the radial ball bearing. Accordingly, even if the oil jet nozzle is provided in the second main bearing section into which the radial roller bearing is fitted, the distance from the crankshaft center to the attachment position of the oil jet can be decreased and the engine itself can be reduced in size.

Abstract: An oil sump for lubricating oil is provided at a lower part of a crank chamber of a dry sump-type four-cycle engine. A reed valve is provided at an outlet of the oil sump which opens when pressure in the crank chamber is high. Furthermore, an oil passage slopes upwards from the outlet of the oil sump, with an outlet of the oil passage being provided above an oil surface level of oil accumulated within the engine. Oil from the outlet of the oil passage is smoothly discharged from the outlet of the oil passage without being discharged into the collected oil. Furthermore, oil mixed with air within the crank chamber is not directly mixed into the collected oil and oil oxidation is therefore prevented. Since there is no direct contact with high-temperature blow-by gas, etc., oil deterioration is suppressed.

Abstract: An exhaust control device for a two-cycle engine which does not impart a change of a shape of an exhaust passage. An exhaust control device is provided in an exhaust port opening to an inner peripheral surface of a cylinder hole of a two-cycle engine wherein a cylinder wall portion adjacent to the exhaust port is formed with a rotational face obtained by rotating an arc having substantially the same curvature as the inner peripheral surface of the cylinder hole about a rotational axis C.sub.1 extending at a right angle to an axis C of the cylinder hole in the outside of the cylinder hole and a recess defined by both ends at a right angle to the rotational axis C.sub.1 and in communication with the exhaust port.

Abstract: A fuel injection quantity control device for use with a two cycle engine being rotatably driven by receiving a fuel-air mixture injected into the engine based on fuel injection quantity instruction signals and the air supplied through an intake passage and ignition of the fuel-air mixture in a combustion chamber includes a rotational speed Ne detection device for detecting the rotational speed Ne of the two cycle engine and for generating a rotational speed Ne signal. An opening .THETA. detection device is provided for detecting the opening .THETA. of a throttle provided in an intake passage for regulating the supply of air and for generating an opening .THETA. signal. A basic injection quantity setting device is provided for setting a basis injection quantity of the fuel based on the rotational speed, Ne signal and the opening .THETA. signal.

Abstract: A fuel injection controlling device for a two-cycle engine includes an electronic fuel injection system having a fuel injection quantity determining device for determining a fuel injection amount in response to rotational speed and throttle opening of the engine. At engine start, the controlling device, in response to operation of an engine kick starter, sequentially decreases starting fuel amount as the number of actuations of the kick starter increases. Fuel injection amount is also decreased in response to increasing engine temperature.