Yamaha 25BMH User manual

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CHAPTER 1
GENERAL INFORMATION
IDENTIFICATION ............................................................................................ 1-1
SERIAL NUMBER .................................................................................... 1-1
STARTING SERIAL NUMBERS ............................................................... 1-1
SAFETY WHILE WORKING ........................................................................... 1-2
FIRE PREVENTION .................................................................................. 1-2
VENTILATION .......................................................................................... 1-2
SELF-PROTECTION ................................................................................. 1-2
OILS, GREASES AND SEALING FLUIDS ............................................... 1-2
GOOD WORKING PRACTICES ............................................................... 1-3
DISASSEMBLY AND ASSEMBLY ........................................................... 1-4
SPECIAL TOOLS ............................................................................................ 1-5
MEASURING ........................................................................................... 1-5
REMOVING AND INSTALLING ............................................................... 1-7
FEATURES AND BENEFITS ........................................................................... 1-8
POWER UNIT ........................................................................................... 1-8
IGNITION SYSTEM ................................................................................. 1-9
IGNITION TIMING IN NEUTRAL .......................................................... 1-10
COOLING SYSTEM ................................................................................1-11
TILLER HANDLE .................................................................................... 1-13
BRACKET AND BOTTOM COWLING ................................................... 1-14
TECHNICAL TIPS ......................................................................................... 1-15
CARBURETOR ....................................................................................... 1-15
IGNITION SYSTEM ............................................................................... 1-18

IDENTIFICATION
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1
IDENTIFICATION
SERIAL NUMBER
The outboard motor’s serial number is
stamped on a label which is attached to the
port clamp bracket.
NOTE:
As an antitheft measure, a special label on
which the outboard motor’s serial number
is stamped is bonded to the port clamp
bracket. The label is specially treated so
that peeling it off causes cracks across the
serial number.
1
Model name
2
Approval model code
3
Transom height
4
Serial number
STARTING SERIAL NUMBERS
The starting serial number blocks are as fol-
lows:
Model name Approval
model code
Starting serial
number
Worldwide
25BMH 61R S:020101
L:350101
30HMH 61T S:050101

SAFETY WHILE WORKING
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SAFETY WHILE WORKING
The procedures given in this manual are
those recommended by Yamaha to be fol-
lowed by Yamaha dealers and their
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 indoors,
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.

SAFETY WHILE WORKING
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Under normal conditions or use, there
should be no hazards from the use of the
lubricants mentioned in this manual, but
safety is all-important, and by adopting
good safety practices, any risk is minimized.
A summary of the most important precau-
tions is as follows:
1. While working, maintain good stan-
dards of personal and industrial
hygiene.
2. Clothing which has become contami-
nated with lubricants should be
changed as soon as practicable, and
laundered before further use.
3. Avoid skin contact with lubricants; do
not, for example, place a soiled wiping-
rag in your pocket.
4. Hands and any other part of the body
which have been in contact with lubri-
cants or lubricant-contaminated cloth-
ing, should be thoroughly washed with
hot water and soap as soon as practica-
ble.
5. To protect the skin, the application of a
suitable barrier cream to the hands
before working, is recommended.
6. A supply of clean lint-free cloths should
be available for wiping purposes.
GOOD WORKING PRACTICES
1. The right tools
Use the recommended special tools to
protect parts from damage. Use the
right tool in the right manner - do not
improvise.
2. Tightening torque
Follow the tightening torque instruc-
tions. When tightening bolts, nuts and
screws, tighten the large sizes first, and
tighten inner-positioned fixings before
outer-positioned ones.

SAFETY WHILE WORKING
GEN
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3. Non-reusable items
Always use new gaskets, packings, O-
rings, split-pins, circlips, etc., on reas-
sembly.
DISASSEMBLY AND ASSEMBLY
1. Clean parts with compressed air when
disassembling.
2. Oil the contact surfaces of moving parts
before assembly.
3. After assembly, check that moving parts
operate normally.
4. Install bearings with the manufacturer’s
markings on the side exposed to view,
and liberally oil the bearings.
5. When installing oil seals, apply a light
coating of water-resistant grease to the
outside diameter.

SPECIAL TOOLS
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SPECIAL TOOLS
Using the correct special tools recom-
mended by Yamaha, will aid the work and
enable accurate assembly and tune-up.
Improvising and using improper tools can
damage the equipment.
MEASURING
1
Dial gauge set
P/N. 90890-01252
2
Crank stand alignment
P/N. 90890-03107
3
Pocket tester
P/N. 90890-03112
4
Timing light
P/N. 90890-03141
5
Compression Gauge
P/N. 90890-03160
6
Peak voltage adaptor
P/N. 90890-03172
7
Digital circuit tester
P/N. 90890-03174
8
Ignition tester
P/N. 90890-06754
9
Vacuum/pressure pump gauge set
P/N. 90890-06756
10
Digital tachometer
P/N. 90890-06760
11
Leakage tester
P/N. 90890-06762
12
Digital caliper
P/N. 90890-06704
1 2
3 4
5 6
7 8
910
11 12

SPECIAL TOOLS
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Cylinder gauge
P/N. 90890-06759
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Outside micrometer
P/N. 90890-03006
P/N. 90890-03008
15
Inside micrometer
P/N. 90890-03010
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Thickness gauge
P/N. 90890-03079
17
Shimming plate
P/N. 90890-06701
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Pinion height gauge
P/N. 90890-06702
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Magnet base
P/N. 90890-06705
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Backlash indicator
P/N. 90890-06706
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Magnet base plate
P/N. 90890-07003
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15 16
17 18
19 20
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SPECIAL TOOLS
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REMOVING AND INSTALLING
1
Flywheel puller
P/N. 90890-06521
2
Flywheel holder
P/N. 90890-06522
3
Small end bearing installer
P/N. 90890-06527
4
Bearing separator
P/N. 90890-06534
5
Stopper guide plate
P/N. 90890-06501
6
Bearing housing puller claw
P/N. 90890-06564
7
Center bolt
P/N. 90890-06504
8
Drive shaft holder 3
P/N. 90890-06517
9
Bearing puller ass’y
P/N. 90890-06535
10
Stopper guide stand
P/N. 90890-06538
11
Driver rod LL
P/N. 90890-06605
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Driver rod LS
P/N. 90890-06606
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Driver rod L3
P/N. 90890-06652
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Driver rod SL
P/N. 90890-06602
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Driver rod SS
P/N. 90890-06604
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Bearing depth plate
P/N. 90890-06603
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Needle bearing attachment
P/N. 90890-06608
P/N. 90890-06611
P/N. 90890-06615
18
Ball bearing attachment
P/N. 90890-06633
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Bearing inner race attachment
P/N. 90890-06643
P/N. 90890-06644
P/N. 90890-06645
20
Bearing outer race attachment
P/N. 90890-06622
P/N. 90890-06628
1 2
3 4
5 6
7 8
910
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13 14
15 16
17 18
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FEATURES AND BENEFITS
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FEATURES AND BENEFITS
POWER UNIT
The 25B and 30H engines are designed to provide superior fuel economy, serviceability, and
durability.
They are based on the previous 25V and 30G with newly designed linkage that controls both
throttle opening and ignition timing mechanically and simultaneously.
Special attention was paid on the crankshaft bearings. Collar is added to the upper main
journal of the crankshaft. Roller bearing is applied to the center bearing.
The collar added on the upper main journal contributes to get better serviceability.
Fig. 2
Fig. 1

FEATURES AND BENEFITS
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IGNITION SYSTEM
Ignition system on the 25B and 30H consists of flywheel magnet, charge coil, pulser coil, CDI
unit, and ignition coil.
Similar to the previous 25V and 30G, the engine has the mechanical ignition timing advance
system that works by way of the linkage.
Superior fuel economy is attained by the modified ignition timing control arrangement.
Also the system restricts the ignition timing advance when the shift is in neutral, which helps
to prevent the kickback at the engine start.
Fig. 3

FEATURES AND BENEFITS
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IGNITION TIMING IN NEUTRAL
As the throttle is opened while the shift in neutral, the Lever moves to the right until it
touches the Arm , and ignition timing advance is stopped at the point "A".
The Arm moves to the right or to the left when the shift is engaged, since it is interlocked
with the shift lever. Thus, when the shift is engaged, the Lever does not touch the Arm
at the point "A", allowing ignition timing advance to take place.
Fig. 5
a
b
b
a b
Fig. 4

FEATURES AND BENEFITS
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COOLING SYSTEM
New structure applied to the cooling system provides additional cooling capacity in the upper
casing.
With additional cooling water passage (indicated by ), water walls contained in the new
upper casing contribute to the reduction of outer surface temperature.
Fig. 6

FEATURES AND BENEFITS
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COOLING SYSTEM
Fig. 7

FEATURES AND BENEFITS
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TILLER HANDLE
For the throttle grip on the steering handle of the 25B and 30H, 100 degrees of opening angle
covers all ranges from full-close to wide-open positions.
Also, new steering handle parts were developed to assume the long use. Inner diameter of
the steering handle engagement area, and both inner and outer diameters of steering bracket
are increased.
Please note that if the new steering handle is installed on the previous models, Steering
handle 2, Steering bracket, Collar, and Washer must be replaced.
Fig. 9
100 degrees
90 degrees
Fig. 8

FEATURES AND BENEFITS
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BRACKET AND BOTTOM COWLING
The Bracket 1 is modified on the 25B and 30H, and newly designed rubber seal is added to
provide better sealing ability for the bottom cowling.
Fig. 10

TECHNICAL TIPS
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TECHNICAL TIPS
CARBURETOR
(1) Slow air jet (idling and slow speed operation)
Since the throttle valve is almost closed at low speeds, and thus the vacuum at venturi is
small, air/fuel mixture is not delivered through the main nozzle.
At idling, the fuel delivered from the pilot jet is mixed with the air delivered from the pilot air
jet.
Air and fuel mixed at the rate determined by the pilot screw adjustment, are supplied to the
engine through the pilot outlet located above the throttle valve.
Once the throttle valve is opened to go beyond the bypass holes during the slow-speed
operation, air/fuel mixture is fed through the bypass holes.
Fig. 11

TECHNICAL TIPS
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(2) Mid range
As the throttle valve opens in the mid-speed range, air/fuel mixture is fed through the bypass
holes in addition to the delivery through the pilot outlet.
Air/fuel mixture is also delivered through the main nozzle depending on the throttle valve
opening.
Fig. 12

TECHNICAL TIPS
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(3) High engine speed
In the high engine speed where the throttle valve is fully open, the fuel delivered through the
main jet is mixed with the air delivered through the main air jet, which is fed into the venturi
through the main nozzle.
Air/fuel mixture delivery through the bypass holes and the pilot outlet continues in the high
engine speed.
Fig. 13

TECHNICAL TIPS
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IGNITION SYSTEM
The 25B and 30H use the mechanical ignition timing advance system, in which the base of the
charge coil and the pulser coil slides in accordance with the throttle valve opening.
Mechanical ignition timing advance applied in this system makes it easier to adjust and
confirm the appropriate ignition timing.
In addition, the ignition timing advance is restricted when the shift is in neutral, which helps
to prevent the kickback at the engine start.
Fig. 15
Fig. 14