Mercury 75 Pro XS FourStroke Operation Maintenance Installation Warranty Manual page 113

OUTBOARD INSTALLATION
FUEL SUPPLY MODULE PRIMING PROCEDURE
The fuel supply module (FSM) is not vented to the ambient air. The air trapped
in the FSM, fuel lines, and fuel rail, will be slightly compressed during the initial
ignition key on with a dry or drained fuel system. Additional key on events
under these conditions, will not compress the air further to finish the priming of
the FSM. Excessive number of key on events may eventually damage the fuel
pumps. The volume of air trapped in the FSM must be purged to prime the fuel
system. This can be achieved by connecting a tool to the fuel rail Schrader
valve fitting to quickly purge the system into an approved container, or by
cranking the engine.
Priming the FSM with a Fuel Pressure Gauge
The use of a purge tool for priming the FSM is the preferred method, but is not
always practical. The objective is to purge the air entrained in the fuel system
through a purge tool connected to the fuel rail Schrader valve test port. During
the key on, opening the dump valve will allow the air to be purged from the
FSM and fuel rail. This method should be used on vessels where the fuel inlet
system to the outboard is restrictive; contains an anti‑siphon valve or holds a
relatively large volume of fuel because of a long fuel supply line or water
separating fuel filter. If a primer bulb is installed, it can be used during the
priming event to shorten the amount of time required to start the engine.
1. Verify the engine is in a level vertical position.
2. Verify the vessel fuel supply line is connected to the outboard fuel system
inlet fitting.
3. Connect a fuel pressure gauge to the fuel rail Schrader valve.
Fuel Pressure Gauge Kit
eng
2807
103
91‑881833A03
Tests the fuel pump pressure; can be
used to relieve fuel pressure.