1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 101Get this manual
6If you suspect the anti-siphon valve, perform these tests Remove anti-siphon valve from fuel tank and install adaptors and clear hose as shown Fill clear hose with water until "X" dimension is 20 in(500 mm)Water must not run through valve Increase water level until "X" dimension is 25 in(630 mm)Water must begin to run through valve before reaching 25 in(630 mm)7If your reading is less than inHg and air bubbles are visible in the clear hose, check entire boat fuel system for air leaksRemember, an air leak into fuel supply system might not create visible fuel leak8If your reading is less than inHgand no bubbles are visible, move the clear hose to the output side of the in-line fuel filter Start engine and run at full throttle If bubbles appear, test in-line fuel filter If no bubbles appear, go to Step 99If no bubbles appear in Step 8, remove the clear hose and install 0-15 PSI (0-103 kPa) fuel pressure gauge between VRO unit and carburetorsHose-