Mercury Optimax 115 Service Manual page 143

FUEL PUMP
CHECKING for RESTRICTED FUEL FLOW CAUSED by
ANTI-SIPHON VALVES
While anti-siphon valves may be helpful from a safety stand-point, they clog with debris,
they may be too small, or they may have too heavy a spring. Summarizing, the pressure
drop across these valves can, and often does, create operational problems and/or pow-
er-head damage by restricting fuel to the fuel pump and VST. Some symptoms of re-
stricted (lean) fuel flow, which could be caused by use of an anti-siphon valve, are:
1 - Loss of fuel pump pressure
2 - Loss of power
3 - High speed surging
4 - Preignition/detonation (piston dome erosion)
5 - Outboard cuts out or hesitates upon acceleration
6 - Outboard runs rough
7 - Outboard quits and cannot be restarted
8 - Outboard will not start
9 - Vapor lock
Since any type of anti-siphon device must be located between the outboard fuel inlet and
fuel tank outlet, a simple method of checking [if such a device (or bad fuel) is a problem
source] is to operate the outboard with a separate fuel supply which is known to be good,
such as a remote fuel tank.
If, after using a separate fuel supply, it is found that the anti-siphon valve is the cause of
the problem, there are 2 solutions to the problem; either 1) remove the anti- siphon valve
or 2) replace it with a solenoid-operated fuel shut off valve.
Page 3A-4 90-855347R1 JANUARY 1999