Chrysler 100, 115 and 140 HP Outboard Motors Service Manual, OB 3439, Page 32Get this manual
Subsection
_ FUELSYSTEM
GENERAL
The fuel system, as defined by this manualincludes all the fuel components common to the system of the motorThese components are the Fuel tank, Fuel pump, Carburetor and Reed valve Troubleshooting and brief description of the operation of the fuel system are covered in this subsectionThe reduction of air pressure causes the fuel to be pushed into and mix with the incoming air stream to form combustible air fuel mixtureThe air fuel mixture is admitted to the crankcase of the motor by reed type inlet valves The reed valve operates automatically, opening when the pressure in the crankcase is low enough so the outside pressure can overcome the reed tensionFigure 1
OPERATION
The fuel tank is non-pressurized and suction operated diaphragm-displacement type fuel pump on the motor draws fuel from the tank and sends it to the carburetor bowls The upstroke of the piston in the cylinder creates suction which draws air through the throat of the carburetorA restriction in the throat, called venturi, acts to reduce air pressure at this point (increasing air velocity