Yamaha F 25 Manual

							Maintenance
36
EMU28874Maintenance chart (additional)
EMU28931Greasing
Yamaha marine grease (Water resistant grease)
EMU28952Cleaning and adjusting spark plug
WARNING
EWM00560
When removing or installing a spark plug,
be careful not to damage the insulator. A
damaged insulator could allow external
sparks, which could lead to explosion orfire.
The spark plug is an important engine compo-
nent and is easy to inspect. The condition of
the spark plug can indicate something about
the condition of the engine. For example, if the
center electrode porcelain is very white, this
could indicate an intake air leak or carburetion
Item ActionsEvery
500 hours (2.5 years) 1000 hours (5 years)
Exhaust guide, exhaust 
manifoldInspection / replace-
ment
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							Maintenance
37
problem in that cylinder. Do not attempt to di-
agnose any problems yourself. Instead, take
the outboard motor to a Yamaha dealer. You
should periodically remove and inspect the
spark plug because heat and deposits will
cause the spark plug to slowly break down
and erode. If electrode erosion becomes ex-
cessive, or if carbon and other deposits are
excessive, you should replace the spark plug
with another of the correct type.
Before fitting the spark plug, measure the
electrode gap with a wire thickness gauge;
adjust the gap to specification if necessary.
When fitting the plug, always clean the gasket
surface and use a new gasket. Wipe off any
dirt from the threads and screw in the spark
plug to the correct torque.NOTE:
If a torque-wrench is not available when you
are fitting a spark plug, a good estimate of the
correct torque is 1/4 to 1/2 a turn past finger-
tight. Have the spark plug adjusted to the cor-
rect torque as soon as possible with a torque-
wrench.
EMU28962Checking fuel system
WARNING
EWM00060
Gasoline and its vapors are highly flam-
mable and explosive. Keep away from
sparks, cigarettes, flames, or other sourc-
es of ignition.
WARNING
EWM00910
Leaking fuel can result in fire or explosion.

Check for fuel leakage regularly.

If any fuel leakage is found, the fuel sys-
tem must be repaired by a qualified me-
chanic. Improper repairs can make the
outboard unsafe to operate.
Check the fuel lines for leaks, crack, or mal-
function. If a problem is found, your Yamaha
dealer or other qualified mechanic should re-
pair it immediately.
Checkpoints

Fuel system parts leakage

Fuel line joint leakage Standard spark plug:
BR6HS
1. Spark plug gap
2. Spark plug I.D. mark (NGK)
Spark plug gap:
0.6–0.7 mm (0.024–0.028 in)
Spark plug torque:
25.0 Nm (18.4 ft-lb) (2.55 kgf-m)
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							Maintenance
38

Fuel line cracks or other damage

Fuel connector leakageEMU29041Inspecting idling speed
WARNING
EWM00451

Do not touch or remove electrical parts
when starting or during operation.

Keep hands, hair, and clothes away from
the flywheel and other rotating parts
while the engine is running.
CAUTION:
ECM00490
This procedure must be performed while
the outboard motor is in the water. A flush-
ing attachment or test tank can be used.
A diagnostic tachometer should be used for
this procedure. Results may vary depending
on whether testing is conducted with the
flushing attachment, in a test tank, or with the
outboard motor in the water.
1. Start the engine and allow it to warm up
fully in neutral until it is running smoothly.
NOTE:
Correct idling speed inspection is only possi-
ble if the engine is fully warmed up. If not
warmed up fully, the idle speed will measure
higher than normal. If you have difficulty veri-
fying the idle speed, or the idle speed requires
adjustment, consult a Yamaha dealer or other
qualified mechanic.
2. Verify whether the idle speed is set to
specification. For idle speed specifica-
tions, see page 30.
EMU30222Changing engine oil
WARNING
EWM00760

Avoid draining the engine oil immediate-
ly after stopping the engine. The oil is
hot and should be handled with care to
avoid burns.

Be sure the outboard motor is securely
fastened to the transom or a stable
stand.
CAUTION:
ECM00970

Do not overfill the oil, and be sure the
outboard motor is upright (not tilted)
when checking and changing the engine
oil.

If the oil level is above the upper level
mark, drain until the level meets the
specified capacity. Overfilling the oil
could cause leakage or damage.
CAUTION:
ECM01240
Change the engine oil after the first 10
hours of operation, and every 100 hours or
at 6-month intervals thereafter. Otherwise
the engine will wear quickly.
NOTE:
Change the engine oil when the oil is still
warm.
1. Put the outboard motor in an upright po-
sition (not tilted).
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							Maintenance
39
2. Prepare a suitable container that holds a
larger amount than the engine oil capaci-
ty. Loosen and remove the drain screw
while holding the container under the
drain hole. Then remove the oil filler cap.
Let the oil drain completely. Wipe up any
spilled oil immediately.
3. Put a new gasket on the oil drain screw.
Apply a light coat of oil to the gasket and
install the drain screw.
NOTE:
If a torque wrench is not available when you
are installing the drain screw, finger tighten
the screw just until the gasket comes into con-
tact with the surface of the drain hole. Thentighten 1/4 to 1/2 turn more. Tighten the drain
screw to the correct torque with a torque
wrench as soon as possible.
4. Add the correct amount of oil through the
filler hole. Install the filler cap.
5. Start the engine and watch to make sure
the low oil pressure warning indicator (if
equipped) turns off. Make sure that there
are no oil leaks.
CAUTION:
ECM00680
If the low oil pressure warning indicator
does not turn off or if there are oil leaks,
stop the engine and find the cause. Con-
tinued operation with a problem could
cause severe engine damage. Consult
your Yamaha dealer if the problem cannot
be located and corrected.
6. Turn off the engine and wait 3 minutes.
Recheck the oil level using the oil level
check window to be sure the level falls
between the upper and lower marks. Fill
1. Drain screw
Drain screw tightening torque:
18.0 Nm (13.3 ft-lb) (1.84 kgf-m)
Recommended engine oil:
4-stroke outboard motor oil
Engine oil quantity (excluding oil filter):
0.35 L (0.37 US qt) (0.31 Imp.qt)
1. Oil filler cap
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							Maintenance
40
with oil if it is below the lower mark, or
drain to the specified level if it is above
the upper mark.
7. Dispose of used oil according to local
regulations.
NOTE:

For more information on the disposal of
used oil, consult your Yamaha dealer.

Change the oil more often when operating
the engine under adverse conditions such
as extended trolling.
EMU29112Checking wiring and connectors

Check that each grounding wire is properly
secured.

Check that each connector is engaged se-
curely.
EMU29120Exhaust leakage
Start the engine and check that no exhaust
leaks from the joints between the exhaust
cover, cylinder head, and body cylinder.
EMU29130Water leakage
Start the engine and check that no water
leaks from the joints between the exhaust
cover, cylinder head, and body cylinder.
EMU29140Engine oil leakage
Check for oil leaks on the around the engine.
NOTE:
If any leaks are found, consult your Yamaha
dealer.
EMU29171Checking propeller
WARNING
EWM00321
You could be seriously injured if the en-
gine accidentally starts when you are near
the propeller.

Before inspecting, removing, or install-
ing the propeller, remove the spark plug
caps from the spark plugs. Also, place
the shift control in neutral, turn the main
switch to “” (off) and remove the key,
and remove the lanyard from the engine
stop switch. Turn off the battery cut-off
switch if your boat has one.

Do not use your hand to hold the propel-
ler when loosening or tightening the
propeller nut. Put a wood block between
the anti-cavitation plate and the propel-
ler to prevent the propeller from turning.
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							Maintenance
41
Checkpoints

Check each of the propeller blades for
wear, erosion from cavitation or ventilation,
or other damage.

Check the propeller shaft for damage.

Check the splines / shear pin for wear or
damage.

Check for fish line tangled around the pro-
peller shaft.

Check the propeller shaft oil seal for dam-
age.
NOTE:
If the shear pin equipped: it is designed to
break if the propeller hits a hard underwater
obstacle to help protect the propeller and
drive mechanism. The propeller will then spin
freely on the shaft. If this happens, the shear
pin must be replaced.
EMU30660Removing the propellerEMU29194Spline models
1. Straighten the cotter pin and pull it out us-
ing a pair of pliers.
2. Remove the propeller nut, washer, and
spacer (if equipped).
3. Remove the propeller and thrust washer.
EMU30670Installing the PropellerEMU30371Spline models
CAUTION:
ECM00340

Be sure to install the thrust washer be-
fore installing the propeller, otherwise
the lower case and propeller boss could
be damaged.

Be sure to use a new cotter pin and bend
the ends over securely. Otherwise the
propeller could come off during opera-
tion and be lost.
1. Apply Yamaha marine grease or a corro-
sion resistant grease to the propeller
shaft.
1. Cotter pin
2. Propeller nut
3. Washer
4. Propeller
5. Thrust washer
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							Maintenance
42
2. Install the spacer (if equipped), thrust
washer, and propeller on the propeller
shaft.
3. Install the spacer (if equipped) and the
washer. Tighten the propeller nut until
there is no forward-and-backward move-
ment.
4. Align the propeller nut with the propeller
shaft hole. Insert a new cotter pin in the
hole and bend the cotter pin ends.
NOTE:
If the propeller nut does not align with the pro-
peller shaft hole after tightening it, loosen the
nut until it aligns with the hole.
EMU29282Changing gear oil
WARNING
EWM00800

Be sure the outboard motor is securely
fastened to the transom or a stable
stand. You could be severely injured if
the outboard motor falls on you.

Never get under the lower unit while it is
tilted, even when the tilt support lever or
knob is locked. Severe injury could oc-
cur if the outboard motor accidentally
falls.
1. Tilt the outboard motor so that the gear oil
drain screw is at the lowest point possi-
ble.2. Place a suitable container under the gear
case.
3. Remove the gear oil drain screw and gas-
ket.
NOTE:

If a magnetic gear oil drain screw is
equipped, remove all metal particles from
the screw before installing it.

Always use new gaskets. Do not reuse the
removed gaskets.
4. Remove the oil level plug and gasket to
allow the oil to drain completely.
CAUTION:
ECM00710
Inspect the used oil after it has been
drained. If the oil is milky, water is getting
into the gear case which can cause gear
damage. Consult a Yamaha dealer for re-
pair of the lower unit seals.
NOTE:
For disposal of used oil, consult your Yamaha
dealer.
5. With the outboard motor in a vertical po-
sition, and using a flexible or pressurized
filling device, inject the gear oil into the
gear oil drain screw hole.
1. Gear oil drain screw
2. Oil level plug
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							Maintenance
43
6. Put a new gasket on the oil level plug.
When the oil begins to flow out of the oil
level plug hole, insert and tighten the oil
level plug.
7. Put a new gasket on the gear oil drain
screw. Insert and tighten the gear oil
drain screw.
EMU29312Inspecting and replacing anode(s)
Yamaha outboard motors are protected from
corrosion by sacrificial anodes. Inspect the
external anodes periodically. Remove scales
from the surfaces of the anodes. Consult a
Yamaha dealer for replacement of external
anodes.
CAUTION:
ECM00720
Do not paint anodes, as this would render
them ineffective.
NOTE:
Inspect ground leads attached to external an-
odes on equipped models. Consult a Yamaha
dealer for inspection and replacement of inter-
nal anodes attached to the power unit.
EMU29390Checking top cowling
Check the fitting of the top cowling by pushing
it with both hands. If it is loose have it repaired
by your Yamaha dealer.
EMU29400Coating the boat bottom
A clean hull improves boat performance. The
boat bottom should be kept as clean of marine
growth as possible. If necessary, the boat bot-
tom can be coated with an anti-fouling paint
approved for your area to inhibit marine
growth.
Do not use anti-fouling paint which includes
copper or graphite. These paints can cause
more rapid engine corrosion. Recommended gear oil:
Hypoid gear oil SAE#90
Gear oil quantity:
75.0 cm³ (2.54 US oz) (2.65 Imp.oz)
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							Maintenance
44
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							Trouble Recovery
45
EMU29424
Troubleshooting
A problem in the fuel, compression, or ignition
systems can cause poor starting, loss of pow-
er, or other problems. This section describes
basic checks and possible remedies, and cov-
ers all Yamaha outboard motors. Therefore
some items may not apply to your model.
If your outboard motor requires repair, bring it
to your Yamaha dealer.
If the engine trouble warning indicator is flash-
ing, consult your Yamaha dealer.
Starter will not operate.
Q. Is battery capacity weak or low?
A. Check battery condition. Use battery of rec-
ommended capacity.
Q. Are battery connections loose or corrod-
ed?
A. Tighten battery cables and clean battery
terminals.
Q. Is fuse for electric start relay or electric cir-
cuit blown?
A. Check for cause of electric overload and
repair. Replace fuse with one of correct am-
perage.
Q. Are starter components faulty?
A. Have serviced by a Yamaha dealer.
Q. Is shift lever in gear?
A. Shift to neutral.
Engine will not start (starter operates).
Q. Is fuel tank empty?
A. Fill tank with clean, fresh fuel.
Q. Is fuel contaminated or stale?
A. Fill tank with clean, fresh fuel.Q. Is fuel filter clogged?
A. Clean or replace filter.
Q. Is starting procedure incorrect?
A. See page 21.
Q. Has fuel pump malfunctioned?
A. Have serviced by a Yamaha dealer.
Q. Are spark plug(s) fouled or of incorrect
type?
A. Inspect spark plug(s). Clean or replace with
recommended type.
Q. Are spark plug cap(s) fitted incorrectly?
A. Check and re-fit cap(s).
Q. Is ignition wiring damaged or poorly con-
nected?
A. Check wires for wear or breaks. Tighten all
loose connections. Replace worn or broken
wires.
Q. Are ignition parts faulty?
A. Have serviced by a Yamaha dealer.
Q. Is engine stop switch lanyard not at-
tached?
A. Attach lanyard.
Q. Are engine inner parts damaged?
A. Have serviced by a Yamaha dealer.
Engine idles irregularly or stalls.
Q. Are spark plug(s) fouled or of incorrect
type?
A. Inspect spark plug(s). Clean or replace with
recommended type.
Q. Is fuel system obstructed?
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