Abstract: A loop-scavenged, two-cycle internal combustion engine has a low-pressure, cylinder wall fuel injection system that is practical for multi-cylinder marine engines and also reduces the amount of unburned hydrocarbons in exhaust emissions when compared to conventional carbureted two-cycle engines. The fuel injectors are mounted through the cylinder wall so that fuel spray contacts the piston crown underneath a zone in which incoming air flow through the transfer ports converges. The converging air flow helps to convect vaporized fuel from the piston crown upwards towards the spark plug electrode in the combustion chamber and away from the exhaust port, thereby reducing the likelihood of short circuiting unburned fuel through the exhaust port before the exhaust port closes and compression begins. All fuel is injected into the piston cavity before the exhaust port closes.

Abstract: An auxiliary fuel supply system is provided for a two cycle internal combustion engine (302). A first fuel line (350) supplies fuel from the fuel pump (338) to a solenoid (352) which is continuously cyclable between ON and OFF states during running of the engine, includig high speed operation where detonation may occur. Fuel then flows through a second fuel line (354) to a restriction orifice metering housing (356), and then to a plurality of third branch fuel lines (358, 384, 386, 388, 390 and 392) for delivery to respective cylinders. The restriction orifices provide a pressure drop from the second fuel line to the plurality of third fuel lines, to provide lower fuel pressure in the third fuel lines, to reduce the chance of leakage at the intake manifold (326), and also to reduce fuel pressure fluctuations in the third fuel lines otherwise due to cycling of the solenoid. Metering housing structure is disclosed.

Abstract: A cold start fuel enrichment circuit for an internal combustion engine includes a thermistor (204) sensing engine temperature, a voltage source (V.sub.DD) continually biasing the thermistor such that the voltage across the thermistor continually varies with engine temperature and provides an output fuel enrichment signal, and a circuit (218, 220) connecting the engine battery (206) through the start switch (208) to the thermistor to additionally bias the thermistor during cranking of the engine. A combination cold start and knock prevention fuel enrichment circuit is also provided.