1971 Evinrude Fisherman 6HP outboards Service Manual, Page 15Get this manual
DESCRIPTION FUEL FLOW The HP Model fuel system consists of fuel tank, fuel pump, and carburetorThe fuel tank is nonpressurized, suction operatedA diaphragm-displacement type fuel pump on the motor draws fuel from the tank and furnishes it to the carburetor through fuel filterI NDU CE LOW PR SSU RE EN TURI
THEORY OF OPERATION
The carburetor is metering device for mixing fuel and airAt idle speed, an engine requires mixture of about parts air to part fuelHigh speed mixture is about 12:1A small chamber holds the fuelA float valve admits fuel from the fuel tank to replace fuel as it is consumed by the engineMetering jets in the carburetor throat extend down into the fuel chamberThe upstroke of the piston in the cylinder creates suction that draws air through the throatA restriction in the throat, called venturi, has the effect of reducing air pressure at this point by controlling air velocityThe differential in throat and chamber air pressures causes the fuel to be pushed out of the metering jets and into the air streamHere it mixes with the air to form combustible mixture for exploding in the engine cylindersIn order to mix the fuel and air in just the right