Abstract: A porous member is disposed within the exhaust stream of a marine engine at a location where its temperature approximates the temperature of the exhaust stream through normal use of the engine. Exhaust gas flows freely through the non-catalytic porous member, but water passing in a reverse direction through the exhaust system is vaporized as it attempts to flow through the non-catalytic porous member.

Abstract: A method for operating a marine engine uses four valves to control the flow of secondary air that is inducted into each of the cylinders of an engine. An oxygen sensor is disposed in an exhaust passage downstream from the cylinders and upstream from a catalytic converter. A carburetor is calibrated to provide a richer than stoichiometric air/fuel ratio so that inducted secondary air through the valves associated with each cylinder can result in a stoichiometric ratio of air flowing into each cylinder. The cylinders are each provided with their own valve in order to allow the air/fuel ratios to be equalized for each cylinder regardless of the configuration and geometry of the intake manifold and its associated conduits.

Abstract: A switching mechanism capable of switching between a two-stroke and a four-stroke operation of an engine as desired, wherein the switching mechanism is switchable between engagement with a first cam lobe for four-stroke operation and a second cam lobe for two-stroke operation, the four-stroke operation maximizing fuel and emissions efficiency and the two-stroke operation maximizing power.

Abstract: A switching mechanism capable of switching between a two-stroke and a four-stroke operation of an engine as desired, wherein the switching mechanism is switchable between engagement with a first cam lobe for four-stroke operation and a second cam lobe for two-stroke operation, the four-stroke operation maximizing fuel and emissions efficiency and the two-stroke operation maximizing power.

Abstract: An exhaust gas flow circuit includes a pumping unit having an inlet communicating with the exhaust system, and an exhaust outlet, for pumping exhaust gas from the exhaust system to the exhaust outlet. A bypass passage is arranged in parallel flow relation with the pumping unit between the inlet and outlet. When the mass flow rate of exhaust gas is relatively high, a bypass valve opens the bypass passage providing a flow path for exhaust gas between the inlet and outlet in parallel with the pumping unit. When the mass flow rate of exhaust gas is relatively low, the bypass valve closes the bypass passage. The bypass valve can be controlled to open and close in response to engine speed or mass flow rate of exhaust gas, for example.