1997 Johnson Evinrude "EU" 90 thru 115 90 CV Service Manual, P/N 507267, Page 58Get this manual
Testing Fuel System Purpose
The following procedure is designed to help you isolate defective component in the boat or engine fuel systemThe 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
To avoid accidental starting of engine while changing propellers, twist and remove all spark plug leads
INote Some checks require that the engine be run at full throttle
under loadInstall the correct test propeller and run the engine in suitable test tank1Start engine and allow it to reach normal operating temperature
INote Push
fuel hose off fuel fittingsdon't pullIf pushing won't separate hose and fitting, carefully cut the hose along its side and peel it back to avoid damaging the fittings
2Install ONIC Vacuum Gauge, PIN 390954or 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 leakageelectric fuel primer pump to restart engineFuel system pressure could cause immediate damage to vacuum gauge3Start engine and run at full throttle for at least two minutesMonitor clear vinyl hose for signs of air or vapor bubbles and note reading on vacuum gauge4The vacuum gauge reading must not exceed inches 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 5