147
Fuel System
Fuel System Tests
7
Results:
Normal pressure:
• Perform the Lift Pump Vacuum Test on p. 147.
Make sure no air leaks or restrictions exist in
the fuel supply hose or boat fuel system.
Low pressure:
• Check pulse hoses and fittings for restrictions.
• Perform the Lift Pump Vacuum Test on p. 147.
Make sure no air leaks or restrictions exist in
the fuel supply hose or boat fuel system.
• Check fuel flow through fuel lift pump. Use fuel
primer bulb to force fuel through pump.
No pressure:
• Check pulse hoses and fittings restrictions.
• Check fuel flow through fuel lift pump. Use fuel
primer or primer bulb to force fuel through
pump.
• Momentarily prime or squeeze primer bulb to
check gauge operation.
• Check pulse hose and fittings for restrictions.
Lift Pump Vacuum Test
Confirm fuel supply to the fuel lift pump.
Temporarily install a vacuum gauge, T-fitting, and
8 in. (20.3 cm) of clear vinyl hose between the fuel
supply hose and fuel lift pump (inlet). Secure con-
nections with tie straps to prevent fuel or air leaks.
START outboard and run at FULL THROTTLE for
at least two minutes. Monitor clear vinyl hose for
the presence of air. Air bubbles indicate a faulty
hose, connection, or fuel tank pick-up. Repair, if
necessary, before proceeding.
There should be no air or vapor bubbles visible in
the clear hose. The maximum inlet fuel vacuum
should not exceed 4 in. Hg. (13.5 kPa) at the inlet
to the fuel lift pump under any operating condi-
tions (IDLE to WOT).
A higher vacuum indicates an excessive restric-
tion in the fuel supply. Repair as needed. Refer to
Fuel System Requirements on p. 138 for fuel
supply component requirements.
Lift Pump Diaphragm Test
Perform this test only if a damaged pump is sus-
pected. This test does not confirm the perfor-
mance of internal fuel pump check valves.
Remove the pulse hose from the crankcase fitting.
Apply 15 psi (103 kPa) to the pulse hose of the
pump. Replace lift pump if pump fails to hold pres-
sure.
NOTICE
Do not use fuel primer bulb, manual fuel
primer, or electric fuel pump primer to restart
outboard. A positive pressure in the fuel sup-
ply could damage some vacuum gauges.
000243
1. Pulse fitting
002334a
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