1971 Johnson 125HP outboards Service Manual, Page 19Get this manual
OEseRI PTiON
VENTURI
FUEL FLOW
ATMOSPHERIC AIR PRESSURE
The fuel system consists of fuel tank, fuel pump, and two carburetorsThe fuel tank is non-pressurized, suction operatedA diaphragmdisplacement type fuel pump on the motor draws fuel from the tank and feeds it to the carburetors through fuel filterCARBURETORS Each carburetor is two barrel, side-draft, float feed typeHighspeed jets are fixed, and only the low-speed jets are adjustableThrottle linkage is synchronized with the distributor through an adjustable linkageTHEORY OF OPERATION