Suzuki outboard motors 1988 2003 repair manual., Page 66Get this manual
4-4 FUEL SYSTEM At the carburetor, the fuel passes through the inlet passage to the needle and seat, and then into the float chamber (reservoir)A float in the chamber rides up and down on the surface of the fuelAfter fuel enters the chamber and the level rises to predetermined point, tang on the float closes the inlet needle and the flow entering the chamber is cut offWhen fuel leaves the chamber as the engine operates, the fuel level drops and the float tang allows the inlet needle to move off its seat and fuel once again enters the chamberIn this manner, constant reservoir of fuel is maintained in the chamber to satisfy the demands of the engine at all speedsA fuel chamber vent hole is located near the top of the carburetor body to permit atmospheric pressure to act against the fuel in each chamberThis pressure assures an adequate fuel supply to the various operating systems of the powerhead AirIFuel Mixture
BY-PASS HOLES
MAIN JET
ISee Figure 2
suction effect is created each time the piston moves upward in the cylinderThis suction draws air through the throat of the carburetorA restriction in the throat, called venturi, controls air velocity and has the effect of reducing air pressure at this pointThe difference in air pressures at the throat and in the fuel chamber, causes the fuel to be pushed out of metering jets extending down into the fuel chamberWhen the fuel leaves the jets, it mixes with the air passing through the venturiThis fuellair mixture should then be in the proper proportion for burning in the cylinders for maximum engine performanceIn order to obtain the proper airlfuel mixture for all engine speeds, some models have high and low speed jetsThese jets have adjustable needle valves which are used to compensate for changing atmospheric conditionsIn almost all cases, the high-speed circuit has fixed high-speed jets and are not adjustableA throttle valve controls the flow of airlfuel mixture drawn into the combustion chambersA cold powerhead requires richer fuel mixture to start and during the brief period it is warming to normal operating temperatureA choke valve is placed ahead of the metering jets and venturiAs this valve begins to close, the volume of air intake is reduced, thus enriching the mixture entering the cylindersWhen this choke valve is fully closed, very rich fuel mixture is drawn into the cylindersThe throat of the carburetor is usually referred to as the barrelCarburetors with single, double, or four barrels have individual metering jets, needle valves, throttle and choke plates for each barrelSingle and two barrel carburetors are fed by single float and chamber Fig3 The starting circuit