1998 Johnson Evinrude EC 50 thru 70 HP 3-Cylinder Service Manual, Page 63Get this manual
Description of Outboard Fuel System
The VRO pump assembly is combination mechanical fuel and oil pumps and fueloil mixer powered by crankcase pressure and vacuum pulsesThe VRO pump injects the proper amount of oil into the fuel system
The VRO pump incorporates circuit in the electrical module that warns the operator of "NO OIL" situation
The fuel pump is of the diaphragm-displacement type and is operated by changes in crankcase pressureAlternately, suction and pressure in the crankcase are transmitted to the pump diaphragm