1984-1986 Mercury Force 9.9 and 15HP Outboards Service Manual, Page 10Get this manual
SECTION
FUEL SYSTEM
GENERAL
The fuel system includes the fuel lank, fuel pumpca rburetors and reed valves Troubleshooting and brief description 01 the operation of the fuel system arecQvered in this subsection
TROUBLESHOOTING
GeneralWhen motor will not start because of problem in the fue systemseries of steps can be taken to pinpoint the cause of the trouble Fuel from the tank must reach the combustion chamberAny interruption of this flow will stop the motorThe following suggested check list will help to deter mine the exact cause of the trouble
OPERATION
The fuel tank is non-pressurized diaphragmdisplacement fuel pump on the molor draws fuel from the tank and sends it to the carburetor bowls Piston upstroke creates low pressure which draws ai through the throat of the carburetor restriction (venturi) in the throat reduces ai pressure and increases air velocity Red uction air pressure causes fuel to be drawn into and mixed with the incoming air stream to form the ai r! fue mixture The airfuel ixture enters the ankcase through reed nlet valves The reed valves operate automaticall y, opening when the pressure in the crankcase is low enough to allow outside pressure to overcome reed tension Figure 1