PDF Service Manual Yamaha EK25BMH Outboard - 1 MB
Keep your Yamaha EK25BMH outboard motor in top condition with this official service manual.
This guide provides detailed instructions for maintenance, troubleshooting, and repair.
It covers everything from basic tune-ups to complete engine overhauls, with clear diagrams and specifications.
This manual is essential for both DIY boaters and professional marine mechanics.
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--- Page 1 ---
EK25BMH
SERVICE MANUAL
290404 69T-28197-ZA-11
--- Page 3 ---
GEN
INFO SAFETY WHILE WORKING E
SAFETY WHILE WORKING
The procedures given in this manual are
those recommended by Yamaha to be fol-
l o w e d b y Ya m a h a d e a l e r s a n d t h e i r
mechanics.
FIRE PREVENTION
Gasoline (petrol) is highly flammable.
Petroleum vapor is explosive if ignited.
Do not smoke while handling gasoline and
keep it away from heat, sparks and open
flames.
VENTILATION
Petroleum vapor is heavier than air and is
deadly if inhaled in large quantities. Engine
exhaust gases are harmful to breathe.
When test-running an engine indoor s,
maintain good ventilation.
SELF-PROTECTION
Protect your eyes with suitable safety
glasses or safety goggles, when grinding or
when doing any operation which may cause
particles to fly off. Protect hands and feet by
wearing safety gloves or protective shoes if
appropriate to the work you are doing.
OILS, GREASES AND SEALING
FLUIDS
Use only genuine Yamaha oils, greases and
sealing fluids or those recommended by
Yamaha.
1-2
--- Page 4 ---
GEN
INFO FEATURES AND BENEFITS E
COOLING SYSTEM
Fig. 5
1-12
--- Page 5 ---
SPEC MAINTENANCE SPECIFICATIONS E
ELECTRICAL
Model
Item Unit
Worldwide EK25BMH
IGNITION SYSTEM
Ignition timing
(Full retard) Degree ATDC 2 ± 2
(Full advanced) Degree BTDC 22 ± 2
Spark plug gap mm (in) 0.9 - 1.0 (0.035 - 0.039)
Ignition spark gap
(Minimum) mm (in) 8.0 (0.31)
Ignition coil resistance
(Primary) Ω 0.18 - 0.24
(Secondary) kΩ 2.70 - 3.70
Charge coil resistance
Ω 342 - 418
(Br - L)
Charge coil output peak
voltage (Br - L)
@ cranking 1*1 V 146
@ cranking 2*1 V 146
@ 1,500 r/min V 150
@ 3,500 r/min V 150
Pulser coil resistance
Ω 311 - 381
(W/R - B , W/B - B)
Pulser coil output peak
voltage (W/R - B , W/B - B)
@ cranking 1*1 V 6.8
@ cranking 2*1 V 6.7
@ 1,500 r/min V 16.0
@ 3,500 r/min V 26.0
CDI unit resistance Ω Refer to the "CDI UNIT" on page 8-10
CDI unit output peak voltage
(B/O - B , B/W - B)
@ cranking 1*1 V 5.5
*1
@ cranking 2 V 130.0
@ 1,500 r/min V 135.0
@ 3,500 r/min V 135.0
*1
Cranking 1: Open circuit.
Cranking 2: Related parts are connected.
2-6
--- Page 6 ---
CHK
ADJ TOP COWLING/FUEL SYSTEM E
TOP COWLING
CHECKING THE TOP COWLING FIT
Check:
• Top cowling
Cracks/damage → Replace.
• Hook
Bent → Correct.
• Rivet
Damage → Repair.
• Rubber of trim
Peel/tear → Repair.
NOTE:
Hooks and latches are unadjustable.
FUEL SYSTEM
CHECKING THE FUEL LINE
Check:
• Fuel hose
Cracks/damage/leak → Replace.
Refer to "FUEL JOINT, FUEL FILTER,
AND FUEL PUMP" on page 4-1.
3-2
--- Page 7 ---
CHK
ADJ CONTROL SYSTEM E
(11) Move the throttle 2 to full-close posi-
tion.
(12) At this point, make sure that the throttle
lever is in contact with the throttle stop
screw on the carburetor.
NOTE:
• After adjustment, open and close the
throttle for several times for reassur-
ance.
• If they are not in contact, adjust the car-
buretor control link.
Refer to "Adjusting the carburetor control
link:" on page 3-7.
6. Adjusting the throttle control lever:
• Throttle control lever
Adjustment steps
(1) Set the shift lever 1 at the forward
position.
(2) Move the throttle 2 to full-open posi-
tion.
3-12
--- Page 8 ---
CHK
ADJ GENERAL E
CHECKING THE SPARK PLUGS
1. Check:
• Electrodes 1
Cracks/excessive wear → Replace.
• Insulator color 2
Distinctly different color → Check the
engine condition.
Color guide:
Medium to light tan color
Normal
Whitish color
• Lean fuel mixture
• Plugged jet (s)
• Wrong setting
Blackish color
• Rich mixture
• Excessive oil usage
• Defective ignition system
• Defective spark plug
2. Clean:
• Spark plug
(use a spark plug cleaner or wire
brush)
3. Check:
• Spark plug type 1
Incorrect → Replace.
Standard spark plug
NGK B7HS-10
4. Measure:
• Spark plug gap a
Out of specification → Replace.
Spark plug gap
0.9-1.0 mm (0.035-0.039 in)
3-22
--- Page 9 ---
FUEL FUEL PUMP E
CHECKING THE FUEL PUMP
1. Check:
• Body 1
• Body 2
• Body 3
• Body 4
Cracks/damage/leak → Replace.
Foreign matters → Clean.
• Seat valve 5
Cracks/ damage → Replace.
• Diaphragm 6
Damage → Replace.
2. Check:
• Fuel pump
Reverse air flow → Replace.
Checking steps
NOTE:
Do not overpressurize the fuel pump. Exces-
sive pressure may cause air to leak out.
(1) Install the Vacuum/pressure pump gauge
set onto the fuel pump as shown.
Vacuum/pressure pump gauge set
90890-06756
(2) Apply the specified pressure with the
Vacuam/pressure pump gauge set.
Fuel pump pressure
50 kPa (0.5 kg/cm2, 7.25 psi)
NOTE:
• Make sure no air comes out of the
opposite side of the fuel pump.
• Start the engine and confirm the proper
function.
4-6
--- Page 10 ---
FUEL CARBURETOR E
CHECKING THE CARBURETOR
CAUTION:
Do not use steel-wire to clean the jets. This
may enlarge the jet diameters and seriously
affect performance.
Check:
• Carburetor body 1
Cracks/damage → Replace.
Contamination → Clean.
• Needle valve 2
Grooved wear → Replace.
• Pilot screw 3
25B-4-19
Bent/wear → Replace.
• Main jet
Contamination → Clean.
• Pilot jet
Contamination → Clean.
• Main nozzle
Contamination → Clean.
• Float
Cracks/damage → Replace.
• Pump plunger 4
Cracks/damage → Replace.
• Fuel passage
Clog → Clean.
• Air passage
Clog → Clean.
NOTE:
Use a suitable cleaning solvent and blow
out clogged passages with compressed air.
WARNING
Protect your eyes with suitable safety spec-
tacles or safety goggles when using com-
pressed air.
4-16
--- Page 11 ---
POWR RECOIL STARTER E
DISASSEMBLING THE RECOIL STARTER
Step Job/Parts Q’ty Remarks
1 Starter stop wire 1
2 Starter stop plunger 1
3 Spring 1
4 Cover 1
5 Starter handle-grip 1
6 Damper 1
7 Bolt (with washer) 2
8 Rope guide 1
9 Nut 1
10 Center bolt 1
11 Thrust washer 1
12 Friction plate 1
13 Collar 1 1
Continued on next page.
5-2
--- Page 12 ---
POWR POWER UNIT E
POWER UNIT
DISCONNECTING THE LEADS AND STAYS
Step Job/Part Q’ty Remarks
1 Bolt 4
2 Washer 2
3 Bolt 1
4 Electrical unit 1
5 Bolt 1
6 Earth lead 1
7 Bolt 2
8 Bolt 1
9 Stay 1
10 Bolt 2
11 Stay 1
12 Bolt 1
13 Stay 1
Continued on next page.
5-12
--- Page 14 ---
POWR CYLINDER HEAD E
INSTALLING THE CYLINDER HEAD
AND CYLINDER HEAD COVER
Install:
• Cylinder head 3 and cylinder head
cover 1
NOTE:
• Temporarily assemble; cylinder head
cover 1 , cylinder head cover gasket 2 ,
cylinder head 3 , and cylinder head
gasket 4 in that order, and then install
the assembled parts onto the crank-
case.
• Apply LOCTITE® No.572 on the bolts.
• Tighten the cylinder head mounting
bolts and nut in sequence and in two
steps of torque.
Cylinder head mounting bolts
1st: 15 N • m (1.5 kgf • m, 11 ft• lb)
T.
R.
2nd:30 N • m (3.0 kgf • m, 22 ft • lb)
INSTALLING THE THERMOSTAT
Install:
• Thermostat 1
• Plain washer 2
• Gasket 3
• Thermostat cover 4
• Bolt 5
NOTE:
• Always use the new gasket.
• Tighten the bolts in sequence.
Thermostat cover bolts
8 N • m (0.8 kgf • m, 5.9 ft • lb)
T.
R.
5-22
--- Page 15 ---
POWR CRANKSHAFT AND CYLINDER BODY E
CHECKING THE PISTON PINS AND
SMALL-END BEARINGS
1. Check:
• Piston pin
• Small-end bearing
Heat discoloration → Replace.
Damage/scratches → Replace.
2. Measure:
• Piston pin outside diameter
(use an outside micrometer)
Out of specification → Replace.
Outside micrometer
90890-03006
Piston pin outside diameter
19.895 – 19.900 mm
(0.7833 – 0.7835 in)
3. Measure:
• Piston pin boss inside diameter
(use an inside micrometer)
Out of specification → Replace.
Inside micrometer
90890-03010
Piston pin boss inside diameter
19.904 - 19.915 mm
(0.7836 - 0.7841 in)
5-32
--- Page 16 ---
POWR CRANK SHAFT E
Crank 1 and crank 4 removal
1 Remove:
• Crank 1
• Crank 4
Plate A............................................ 1
90890-02386
Pressure pin B ............................... a
90890-02390
Removing steps
(1) By forcing the pressure pin B a with a
a hydraulic press, remove the crank pin.
(2) When forcing out the crank pin, use care
so that the crankshaft does not fall off.
(3) To remove crank 4, follow the same
procedure.
CAUTION:
• Apply pressure to the pressure pin B a
slowly.
• Hold the pressure pin B a in line with
the press screw spindle.
Crank 2 and crank 3 removal
1 b 1. Remove:
• Crank 2
• Crank 3
Support.......................................... 1
90890-02394
Pressure pin B ............................... a
90890-02390
NOTE:
• Place the pressure pin B a on the crank
2 center shaft b , and force it out using
a press.
• When forcing out the crank pin, use
care so that the crank does not fall off.
5-42
--- Page 18 ---
LOWR PROPELLER SHAFT HOUSING E
DISASSEMBLING THE PROPELLER SHAFT HOUSING
Step Job/Part Q’ty Remarks
1 O-ring 1 Not reusable
2 O-ring 2 Not reusable
3 Reverse gear 1
4 Reverse gear shim *
5 Ball bearing 1
6 Oil seal 2
7 Needle bearing 1
8 Propeller shaft housing 1
9 Washer 1
* As required
6-8
--- Page 19 ---
LOWR LOWER CASE E
LOWER CASE
DISASSEMBLING THE LOWER CASE
Step Job/Part Q’ty Remarks
1 Drive shaft bearing outer race 1
2 Pinion gear shim *
3 Drive shaft sleeve 1
4 Needle bearing 1
5 Tapered roller bearing outer race 1
6 Forward gear shim *
* As required
6-18
--- Page 20 ---
LOWR BACKLASH E
BACKLASH
NOTE:
• Do not install the water pump compo-
nents when measuring the backlash.
• Measure both the forward and reverse
gear backlashes.
• If both the forward and reverse gear
backlashes are larger than specifica-
tion, the pinion gear may be too high.
• If both the forward and reverse gear
backlashes are smaller than specifica-
tion, the pinion gear may be too low.
MEASURING THE FORWARD GEAR
BACKLASH
1. Measure:
• Forward gear backlash
Out of specification → Adjust.
Forward gear backlash
0.31 - 0.72 mm (0.012 - 0.028 in)
Measuring steps
(1) Set the shift rod into the neutral posi-
tion.
(2) Install the propeller shaft housing
puller so it pushes against the propeller
shaft.
Bearing housing puller claw ........ 1
90890-06564
Stopper guide plate ...................... 2
90890-06501
Center bolt..................................... 3
90890-06504
Center bolt
5 N • m (0.5 kgf • m, 3.7 ft • lb)
T.
R.
6-28
--- Page 21 ---
BRKT BOTTOM COWLING E
Step Job/Part Q’ty Remarks
14 Bushing 2
15 Throttle control shaft 1
16 Friction spacer 1
17 Bolt (with washer) 1
18 Clamp lever 2 1
19 Bushing 2
20 Wave washer 1
21 Clamp lever 1 1
7-6
--- Page 22 ---
BRKT UPPER CASE E
CHECKING THE UPPER CASE
Check:
• Upper case 1
Crack/damage → Replace.
• Mount rubber 2
Wear/crack/damage → Replace.
INSTALLING THE UPPER CASE
Install:
• Mount rubber 1 (front upper)
• Mount rubber 2
(side upper) – with gaskets
• Nut 3
• Upper case 4 (to swivel bracket)
• Nut 5 (side upper)
• Mount rubber 6 (side lower)
• Mount rubber 7 (front lower)
• Lower mount cover 8
• Lower mount rubber housing 9
Nut 5
17 N • m (1.7 kgf • m, 13 ft • lb)
T.
R.
Bolt
(lower mount rubber housing 9 )
17 N • m (1.7 kgf • m, 13 ft • lb)
NOTE:
Make sure the lower mount rubber hous-
ing is installed with the “UP” mark point-
ing upward.
7-16
--- Page 23 ---
BRKT CLAMP BRACKETS E
3. Install:
• Clamp bracket 1 (port side)
• Clamp bracket 2 (starboard side)
• Transom clamp handle 3
• Stopper shaft 4
• Stopper knob 5
• Spring pin 6
NOTE:
• Always use the new pin and a spring
pin.
• Apply Yamaha grease A (water resis-
tant grease) to the transom clamp
screw, stopper shaft and the grease
nipple.
4. Install:
• Clamp bracket bolt 1
• Clamp bracket 2 (starboard side)
• Washer 3
• Swivel bracket 4
• Torsion spring 5
• Tilt lever 6
6 • Washer 7
8 • Clamp bracket 8 (port side)
• Nut 9 (clamp bracket bolt)
• Bolt 10
• Collar 11
• Nut 12
• Tilt rod 13 (with conical spring 14 )
• Tension spring 15
5 6
NOTE:
1 Place the tilt lever 6 inside the clamp
bracket 8 (port side) as shown.
Nut 9
45 N • m(4.5 kgf • m, 33 ft • lb)
T.
R.
7-26
--- Page 24 ---
– +
ELEC IGNITION SYSTEM E
CHECKING THE CHARGE COIL
1. Measure:
• Charge coil resistance
Out of specification → Check the
peak voltage.
Charge coil resistance
Br - L
342 - 418 Ω
Measuring steps
(1) Disconnect the Brown (Br) and Blue (L)
leads from the wire harness.
(2) Connect the tester to the charge coil as
shown.
2. Measure:
• Charge coil output peak voltage
Below specification → Replace.
Charge coil output peak voltage
Br – L
Cranking 1,50 0 3 ,5 0 0
r/min
Opened Closed
D.C.V. 146 146 150 150
NOTE:
For the peak voltage measurement, connect
the adaptor as the illustration A for the
open circuit, and as the illustration B for
the closed circuit.
8-8
--- Page 25 ---
TRBL
ANLS E
CHAPTER 9
TROUBLE ANALYSIS
TROUBLE ANALYSIS ..................................................................................... 9-1
TROUBLE ANALYSIS CHART ................................................................. 9-1 1
TROUBLE SHOOTING FOR PEAK VOLTAGE ............................................... 9-4
2
3
4
5
6
7
8
9