Mercury 45 Jet 50-55 Service Manual page 95

PROBLEM 1: ENGINE IDLES ROUGH AND
STALLS
PROBLEM 2: ENGINE RUNS ENEVEN OR
SURGES
PROBLEM 3: ENGINE WILL NOT ACCELERATE.
Possible Cause
A crack in the fuel outlet
tube (located in fuel
tank.)
Anti-Siphon valve re-
stricting fuel flow.
PROBLEM : FUEL BLOW-BACK OUT OF CAR-
BURETOR
Possible Cause
Chipped/Broken (reed-
block) Reeds
PROBLEM : ROUGH IDLE
If related to reed-block,
indicates excessive
preload in reeds.
PROBLEM : CAN'T REDUCE ENGINE RPM TO
SLOW IDLE
Multiple chipped reeds
3A-10 - FUEL SYSTEMS
Corrective Action
Replace.
Refer to "Checking for
Restricted Fuel Flow
Caused by Anti-Si-
phon Valves," follow-
ing.
Corrective Action
Replace Reeds.
Replace Reeds.
Replace Reeds.
CHECKING FOR RESTRICTED FUEL FLOW CAUSED
BY ANTI-SIPHON VALVES
While anti-siphon valves are helpful from a safety stand-
point, they clog, they may be too small, or they may have
too heavy a spring. The pressure drop across these valves
can, create operational problems and/or powerhead dam-
age by restricting fuel. Some symptoms of restricted (lean)
fuel flow, 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
Any type of anti-siphon device must be located between
the outboard fuel inlet and fuel tank outlet. A 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 know to be good.
If, it is found that the anti-siphon valve is the cause of the
problem, either 1) replace the anti-siphon valve or 2) re-
place it with a solenoid-operated fuel shutoff valve.
90-817643R1 DECEMBER 1996