1972 Johnson 4HP Outboard Motor Service Manual, Page 21Get this manual
REASSEMBLV OF CARBURETOR AND LEAF VALVES
Start engine
Allow engine to reaeh normal operating temperature running in tank with test propeller at one-half throttleRun engine at full throttleUsing tachometer, adjust high-speed needle until best high-speed setting is obtainedLOW -SPEED NEEDLE
Attaeh leaf plate to power head using new gaskets both sides of plateSee Figure 3-4Using new gasket, plaee carburetor in position manifold studs and fasten in place with nutsReconneet fuelline to carburetordInstall choke knob
High-speed needle must eorreetly adjusted as described above before low-speed needle adjustment is begunWith motor at operating temperature, run at slow speed (700-750 rpm) with test propeller in tank or boatAdjust low-speed knob until highest rpm reading and smoothest performance are obtainedAllow 15 seconds for motor to respond to adjustmentAdjustment of high-speed needle MUST repeated after final low-speed needle adjustmentfollower Install adjustment knobDO disturb position of needlePosition high speed knob so that the pointer is facing straight and push baek to original position needle valvePosition low speed knob so that the pointer is facing down and push back to original position needle valveWith and needle valve correctly adjusted, motor should idle at 600 THROTTLE TENSION ADJUSTMENT Throttle tension is correct when motor speed mains constant and throttle lever retains its positionadjust throttle tension, tighten the throttle tension screw as requiredSee Figure 3-16