Mercury Optimax 115 Service Manual page 144

Testing Fuel Pump
Install clear fuel hose(s) between fuel pump and VST. Run engine, and inspect fuel pass-
ing thru hose(s) for air bubbles. If air bubbles are found, see "Air Bubbles in Fuel Line,"
below. If air bubbles are NOT found, see "Lack of Fuel Pump Pressure," below.
Low fuel in tank.
Loose fuel line connection.
Fuel pump fitting loose.
A hole or cut in fuel line.
Fuel Pump anchor screw(s) loose.
Fuel Pump filter cover anchor screw loose.
Fuel pump filter gasket worn out.
Fuel pump gasket(s) worn out.
An anti-siphon valve.
Air in fuel line.
A dirty or clogged fuel filter.
The fuel pickup in fuel tank is clogged or dirty.
Worn out fuel pump diaphragm.
Worn out check valve(s) in fuel pump.
A leaky check valve gasket.
Pulse hole(s) plugged.
Hole in pulse hose.
Loose pulse hose.
Excessive fuel hose length.
Fuel hose internal diameter too small.
Primer bulb check valve not opening.
Excessive fuel lift required.
90-855347R1 JANUARY 1999
Problem: Air Bubbles in Fuel Line
Fill tank with fuel.
Check and tighten all connectors.
Tighten fitting.
Check condition of all fuel lines and replace
Tighten all screws evenly and securely.
Tighten screws securely.
Replace gasket.
Rebuild fuel pump.
Problem: Lack of Fuel Pump Pressure
See ''Checking for Restricted Fuel Flow" preced-
ing.
See ''Air Bubbles in Fuel Line", above.
Clean or replace fuel filter.
Clean or replace pickup.
Rebuild fuel pump.
Rebuild fuel pump.
Rebuild fuel pump.
Remove fuel pump and clean out holes.
Replace pulse hose.
Tighten connection(s).
Cut fuel hose to proper length.
Use 5/16 I.D. fuel hose.
Replace primer bulb.
Fuel lift from tank to pump 48 in. (1219.2 mm)
maximum.
FUEL PUMP
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