1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 100Get this manual
Testing VRO System Purpose The following procedure is designed to help you isolate defective component in the boat or engine fuel system The problem might cause loss of engine performance or, if left unrepaired, might cause serious powerhead damageAfter you have isolated the component, refer to Servicing, this Section, for specific repair proceduresTesting Procedure
fTo avoid accidental starting of engine while changing
propellers, twist and remove all spark plug leads
INote Some checksInstall the correctenginepropelleratand run the require that the be run full throttle under loadtest
engine in suitable test tank1Start engine and allow it to reach normal operating temperature2Install OMC Vacuum Gauge PIN 390954 or equivalent and in(20,3 cm) of clear vinyl hose at the fuel inlet fitting on the lower engine coverSecure all connections with tie straps to eliminate air leakageDo not use fU'el primer bulb, manual fuel primer pump or electric fuel primer pump to restart engineFuel system pressure could cause immediate damage to vacuum gauge3Start engine and run at full throttle for at least minutesMonitor clear vinyl hose for signs of air or vapor bubbles and note reading on vacuum gauge4The vacuum gauge reading must not exceed inof mercury (Hg) at any timeThere should be no air or vapor bubbles visible in the clear hose If reading is to inHg and no bubbles are present, go to Step If reading is to inHg and bubbles are present, go to Step If reading exceeds inHg, go to Step 55If your reading exceeds inHg you must test each boat fuel system component for excessive restriction before continuingRefer to Boat Fuel System Recommendations, this Section, for component descriptions