1977 Evinrude 4HP Outboards Service Manual, PN 5303, Page 17Get this manual
LEAF VALVES The leaf valves time the injection of the fuel mixture into the crankcase by opening only when the pressure in the 9rankcase has dropped to predetermined point on the compression strokeSee Figure 3-1CHOKE The carburetor is fitted with manual choke to reduce the ratio of air to fuel for cold startsA choke valve in the air inlet of the barrel is mounted on the choke shaftWhen the choke knob is pushed in, the valve is held open, allowing air to pass freely through the inletWhen the choke knob is pulled out, the valve is closed, restricting the flow of air to the carburetor"""
REMOVAL OF CARBURETOR AND LEAF VALVE ASSEMBLY
aRemove motor coverbPull off high and low speed knobsRemove cotter and hinge pin to remove choke knobSee Figure 3-2