Yamaha FT50C User manual

SERVICE MANUAL
62Y-28197-5A-11
290418
FT50C

NOTICE
This manual has been prepared by Yamaha primarily for use by Yamaha dealers and their trained
mechanics when performing maintenance procedures and repairs to Yamaha equipment. It has
been written to suit the needs of persons who have a basic understanding of the mechanical and
electrical concepts and procedures inherent in the work, for without such knowledge attempted
repairs or service to the equipment could render it unsafe or unfit for use.
Because Yamaha has a policy of continuously improving its products, models may differ in detail
from the descriptions and illustrations given in this publication. Use only the latest edition of this
manual. Authorized Yamaha dealers are notified periodically of modifications and significant
changes in specifications and procedures, and these are incorporated in successive editions of this
manual.
Important information 1
Particularly important information is distinguished in this manual by the following notations:
The Safety Alert Symbol means ATTENTION! BECOME ALERT! YOUR SAFETY IS
INVOLVED!
WARNING
Failure to follow WARNING instructions could result in severe injury or death to the machine
operator, a bystander, or a person inspecting or repairing the outboard motor.
CAUTION:
A CAUTION indicates special precautions that must be taken to avoid damage to the out-
board motor.
NOTE:
A NOTE provides key information to make procedures easier or clearer.
FT50C
SERVICE MANUAL
©2001 by Yamaha Motor Co., Ltd.
1st Edition, June 2001
All rights reserved.
Any reprinting or unauthorized use
without the written permission of
Yamaha Motor Co., Ltd.
is expressly prohibited.
Printed in the Netherlands

Contents
General information 1
GEN
INFO
Specifications 2
SPEC
Periodic checks and adjustments 3
CHK
ADJ
Fuel system 4
FUEL
Power unit 5
POWR
Lower unit 6
LOWR
Bracket unit 7
BRKT
Electrical systems 8
ELEC
Troubleshooting 9
TRBL
SHTG
Index
–+

GEN
INFO
62Y5A11
General information
How to use this manual.................................................................................1-1
Manual format............................................................................................1-1
Symbols.....................................................................................................1-2
Safety while working......................................................................................1-3
Fire prevention...........................................................................................1-3
Ventilation..................................................................................................1-3
Self-protection ...........................................................................................1-3
Parts, lubricants, and sealants ..................................................................1-3
Good working practices .............................................................................1-4
Disassembly and assembly .......................................................................1-4
Identification...................................................................................................1-4
Applicable models .....................................................................................1-4
Serial number ............................................................................................1-4
Features and benefits....................................................................................1-5
Use of leaded gasoline ..............................................................................1-5
Newly designed four carburetors...............................................................1-5
CDI unit with microcomputer .....................................................................1-6
Lower unit ..................................................................................................1-7
Technical tips .................................................................................................1-8
Carburetor .................................................................................................1-8
Acceleration pump...................................................................................1-13
Ignition system.........................................................................................1-15
Ignition timing control...............................................................................1-17
Power trim and tilt....................................................................................1-19
Propeller selection.......................................................................................1-26
Propeller size...........................................................................................1-26
Selection..................................................................................................1-26

62Y5A11
1
2
3
4
5
6
7
8
9
Predelivery checks ......................................................................................1-26
Checking the fuel system ........................................................................1-26
Checking the gear oil...............................................................................1-27
Checking the engine oil ...........................................................................1-27
Checking the battery................................................................................1-27
Checking the outboard motor mounting position .....................................1-27
Checking the remote control cables ........................................................1-27
Checking the steering system .................................................................1-28
Checking the gearshift and throttle operation..........................................1-28
Checking the tilt system...........................................................................1-28
Checking the engine start switch and engine stop switch/
engine shut-off switch ............................................................................1-29
Checking the pilot water outlet ................................................................1-29
Test run ...................................................................................................1-29
Break-in ...................................................................................................1-29
After test run ............................................................................................1-29

GEN
INFO General information
1-1 62Y5A11
How to use this manual 1
Manual format
The format of this manual has been designed to make service procedures clear and easy to under-
stand. Use the information below as a guide for effective and quality service.
1Parts are shown and detailed in an exploded diagram and are listed in the components list.
2Tightening torque specifications are provided in the exploded diagrams and after a numbered
step with tightening instructions.
3Symbols are used to indicate important aspects of a procedure, such as the grade of lubricant
and lubrication point.
4The components list consist of parts and part quantities, as well as bolt screw O-ring and hose
dimensions.
5Service points regarding removal, checking, and installation are shown in individual illustrations
to explain the relevant procedure.
NOTE:
For troubleshooting procedures, see Chapter 9, “Troubleshooting.”

62Y5A11 1-2
1
2
3
4
5
6
7
8
9
Symbols
The symbols below are designed to indicate the content of a chapter.
General information
Specifications
Periodic checks and adjustments
Fuel system
Power unit
Lower unit
Bracket unit
Electrical systems
Troubleshooting
GEN
INFO
SPEC
CHK
ADJ
FUEL
POWR
LOWR
BRKT
ELEC
TRBL
SHTG
–+
Symbols 1to 6indicate specific data.
1Special tool
2Specified oil and fluid
3Specified engine speed
4Specified tightening torque
5Specified measurement
6Specified electrical value
(Resistance, Voltage, Electric current)
Symbols 7to Ain an exploded diagram indicate the grade of lubricant and the lubrication point.
7Apply Yamaha 4-stroke motor oil
8Apply water resistant grease (Yamaha grease A)
9Apply molybdenum disulfide grease
0Apply anti-corrosion grease (Yamaha grease D)
AApply low temperature resistant grease
(Yamaha grease C)
Symbols Bto Gin an exploded diagram indicate the type of sealant or locking agent and the appli-
cation point.
BApply Gasket Maker®
CApply Yamabond No. 4
DApply LOCTITE®No. 271 (Red LOCTITE)
EApply LOCTITE®No. 242 (Blue LOCTITE)
FApply LOCTITE®No. 572
GApply silicon sealant
123456
T
R
.
.
7890A
E
A M D C
BCDEFG
GM
4
271
LT
242
LT
572
LT SS
How to use this manual

GEN
INFO General information
1-3 62Y5A11
Safety while working 1
To prevent an accident or injury and to
ensure quality service, follow the safety pro-
cedures provided below.
Fire prevention
Gasoline is highly flammable.
Keep gasoline and all flammable products
away from heat, sparks, and open flames.
Ventilation
Gasoline vapor and exhaust gas are heavier
than air and extremely poisonous. If inhaled
in large quantities they may cause loss of
consciousness and death within a short time.
When test running an engine indoors (e.g., in
a water tank) be sure to do so where ade-
quate ventilation can be maintained.
Self-protection
Protect your eyes by wearing safety glasses
or safety goggles during all operations involv-
ing drilling and grinding, or when using an air
compressor.
Protect your hands and feet by wearing pro-
tective gloves and safety shoes when neces-
sary.
Parts, lubricants, and sealants
Use only genuine Yamaha parts, lubricants,
and sealants or those recommended by
Yamaha, when servicing or repairing the
outboard motor.
Under normal conditions, the lubricants men-
tioned in this manual should not harm or be
hazardous to your skin. However, you should
follow these precautions to minimize any risk
when working with lubricants.
1. Maintain good standards of personal and
industrial hygiene.
2. Change and wash clothing as soon as
possible if soiled with lubricants.
3. Avoid contact with skin. Do not, for
example, place a soiled rag in your
pocket.
4. Wash hands and any other part of the
body thoroughly with soap and hot water
after contact with a lubricant or lubricant
soiled clothing has been made.
5. To protect your skin, apply a protective
cream to your hands before working on
the outboard motor.

62Y5A11 1-4
1
2
3
4
5
6
7
8
9
6. Keep a supply of clean, lint-free cloths for
wiping up spills, etc.
Good working practices
Special tools
Use the recommended special tools to pro-
tect parts from damage. Use the right tool in
the right manner—do not improvise.
Tightening torques
Follow the tightening torque specifications
provided throughout the manual. When tight-
ening nuts, bolts, and screws, tighten the
large sizes first, and tighten fasteners starting
in the center and moving outward.
Non-reusable parts
Always use new gaskets, seals, O-rings, cot-
ter pins, circlips, etc., when installing or
assembling parts.
Disassembly and assembly
1. Use compressed air to remove dust and
dirt during disassembly.
2. Apply engine oil to the contact surfaces
of moving parts before assembly.
3. Install bearings with a manufacture iden-
tification mark in the direction indicated in
the installation procedure. In addition, be
sure to lubricate the bearings liberally.
4. Apply a thin coat of water-resistant
grease to the lip and out periphery of an
oil seal before installation.
5. Check that moving parts operate nor-
mally after assembly.
Identification 1
Applicable models
This manual covers the following models.
Serial number
The outboard motor serial number is
stamped on a label attached to the port
clamp bracket.
Applicable models
FT50CEHD, FT50CED, FT50CET
Safety while working / Identification

GEN
INFO General information
1-5 62Y5A11
1Model name
2Approved model code
3Transom height
4Serial number
Features and benefits 1
Use of leaded gasoline
New FT50C/F50D is designed for pleasure/light commercial use for all over the world. Therefore,
engine components anti-corrosion and reliability has been increased while regular leaded gasoline
is used.
However, always use regular unleaded gasoline for longer engine life.
Newly designed four carburetors
Newly designed four carburetors have been based on the current F50A. Prime Start has been
adopted for the starting system to further increase starting performance and serviceability. Further-
more, the acceleration pump and the dashpot have been integrated to simplify construction and to
ease serviceability. The four carburetors can be accurately and easily adjusted due to the simple
construction of the links.
1Prime Start
2Acceleration pump
Model name Approved
model code
Starting
serial No.
FT50CEHD
64J
L: 650101–
FT50CED L: 550101–
FT50CET L: 450101–

62Y5A11 1-6
1
2
3
4
5
6
7
8
9
CDI unit with microcomputer
The ignition system consists of a flywheel, stator, pulser coil, thermoswitch, oil pressure switch, CDI
unit, and ignition coil. The CDI unit contains a built-in microcomputer that determines the ignition
timing separately for acceleration and for normal operation, based on signals received from the
pulser coil, thermoswitch, and oil pressure switch.
.
1CDI unit
2Flywheel
3Stator
4Pulser coil
5Thermoswitch
6Ignition coil
7Oil pressure switch
23
4
5
6
7
1
S62Y1210
Identification / Features and benefits

GEN
INFO General information
1-7 62Y5A11
Lower unit
Higher class pinion and gears
The lower unit of the new FT50C uses the same type of large gears that are used in the F100. The
use of the same type of gears that are used in a higher class model provides ample durability, mak-
ing it possible to accommodate a wider range of applications throughout the market.
Pinion Forward gear Reverse gear
Gear ratio
Model Number
of teeth
Diameter
(mm)
Number
of teeth
Diameter
(mm)
Number
of teeth
Diameter
(mm)
F50A 13 45 24 74 24 75 1.8
FT50C 13 46 30 95 30 95 2.3
F50A FT50C S62Y1220K

62Y5A11 1-8
1
2
3
4
5
6
7
8
9
Shift slider type shift mechanism
The FT50C has adopted the shift slider type shift mechanism. This shift mechanism enables a
prompt engagement of the dog clutch regardless of the operating speed of the shift lever. Thus,
smooth and positive shift operation has been made possible.
1Shift rod
2Propeller shaft
3Dog clutch
4Shift slider
ÈForward
ÉReverse
Technical tips 1
Carburetor
Starting system (Prime Start)
To facilitate the starting of a cold engine, an air-fuel mixture that is richer than normal is required.
For this reason, the Prime Start system has been adopted in the FT50C. In the Prime Start system,
the thermo heater plunger is in a position that fully opens the fuel enrichment valve while the engine
is being started. Thus, fuel enrichment is achieved during the starting of the engine, and continues
while the engine is being warmed up. Once the engine starts, current flows from the lighting coil of
the to the thermo heater, allowing the wax in the Prime Start unit to expand. The expanded wax
moves the thermo heater plunger in the direction to close the enrichment valve. As a result, the vol-
ume of fuel that passes through the fuel enrichment valve decreases. A few minutes after the
engine has started, the thermo heater plunger completely closes the fuel enrichment valve, thus
ending the fuel enrichment by the Prime Start system.
Features and benefits / Technical tips

GEN
INFO General information
1-9 62Y5A11
1Prime Start
2Intake manifold of the engine
3Thermo heater plunger
4Fuel enrichment valve
5To carburetor #2 or #4
6Carburetor
7Intake silencer
ÈAir
ÉFuel
ÊPlunger movement
1Prime Start
ÈThe enriched air-fuel mixture is delivered to
cylinders #1 and #2 by the Prime Start system
attached to carburetor #1.
ÉThe enriched air-fuel mixture is delivered to
cylinders #3 and #4 by the Prime Start system
attached to carburetor #3.
:
:
:
S62Y1240K

62Y5A11 1-10
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9
Carburetor operation
1. Idle and low-speed operation
Since the vacuum at the venturi is low when the throttle valve is opened slightly, the main nozzle
does not supply any air-fuel mixture to the engine.
When the engine is operating at idle, the fuel that passes through the pilot jet and the air that passes
through the pilot air jet mix, enabling the air-fuel mixture that has been regulated by the pilot screw
to be fed through the pilot outlet.
Because the throttle valve opens slightly when the engine is operating at low speeds, air-fuel mix-
ture also starts to be fed from the bypass holes.
1Pilot screw
2Pilot outlet
3Bypass holes
4Venturi
5Main nozzle
6Pilot jet
7Main jet
8Pilot air jet
9Main air jet
0Throttle valve
ÈAir
ÉAir-fuel mixture
ÊFuel
3
2
2
1
0
9
8
7
6
5
4
3
:
:
:
S62Y1260
3
2
2
1
0
9
8
7
6
5
4
3
:
:
:
S62Y1260
Technical tips

GEN
INFO General information
1-11 62Y5A11
2. Medium speed operation
When the throttle valve opens further, air-fuel mixture is fed from the pilot outlet and all the bypass
holes. In addition, air-fuel mixture is also supplied from the main nozzle in accordance with the
opening angle of the throttle valve.
1Pilot screw
2Pilot outlet
3Bypass holes
4Venturi
5Pilot jet
6Main jet
7Main nozzle
8Pilot air jet
9Main air jet
0Throttle valve
ÈAir
ÉAir-fuel mixture
ÊFuel
3
2
1
0
9
8
7
6
5
4
3
2
S62Y1270
:
:
:

62Y5A11 1-12
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4
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7
8
9
3. High-speed operation
When the throttle valve approaches its fully open position, the fuel that has been regulated by the
main jet and the air that has been regulated by the main air jet are mixed in the main nozzle. The
resultant mixture is then sprayed by the main nozzle into the venturi. The air-fuel mixture that is
sprayed through the venturi is then fed into the engine.
1Pilot screw
2Pilot outlet
3Bypass holes
4Main nozzle
5Pilot jet
6Main jet
7Main air jet
8Throttle valve
ÈAir
ÉAir-fuel mixture
ÊFuel
:
:
:
S62Y1280
4
5
6
7
8
1
2
3
Technical tips

GEN
INFO General information
1-13 62Y5A11
Acceleration pump
The function of the acceleration pump is to ensure a smooth acceleration by preventing the air-fuel
mixture from becoming temporarily lean in case the throttle valve is opened suddenly. When the
throttle valve is opened suddenly, a large volume of air is introduced into the engine. However,
because fuel is heavier than air, it is not possible to supply the volume of fuel that is necessary for
the large volume of air that has been introduced. Thus, because it is not possible to achieve the air-
fuel mixture that is required by the engine, bucking or hesitation results. For this reason, the acceler-
ation pump temporarily increases the fuel volume in order to adjust the air-fuel mixture to a ratio that
is necessary for the engine in case the throttle valve is opened suddenly.
1Bypass hose
2Acceleration pump
3Pump chamber
4Diaphragm 1
5Throttle lever
ÈAir flow
ÉThrottle valve opening direction
:
:
1
2
3
4
5
S62Y1290

62Y5A11 1-14
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7
8
9
Operation
When the throttle is opened suddenly, diaphragm 1 (via the link that is connected to the throttle
lever) operates to pressurize the air in the pump chamber. The pressurized air opens diaphragm 2,
and becomes distributed to the carburetors by passing through the pipes that are connected to the
carburetors. The pressurized and distributed air then utilizes the passage of the main air jet to flow
into the main nozzle. The pressure of the air helps suck fuel from the main jet, which increases the
fuel in the main nozzle, and thus achieves the fuel enrichment.
1Main air jet
2Main nozzle
3Main jet
4Throttle valve
5Pilot screw
6Pilot outlet
7Pilot jet
8From acceleration pump
9Throttle valve closing
0Throttle valve opening
ADiaphragm 1
BDiaphragm 2
CTo carburetors
ÈAir flow
ÉThrottle valve opening direction
90
1
2
3
1
6
5
4
83
7
2
A
B
A
B
C
S62Y1300
:
:
Technical tips

GEN
INFO General information
1-15 62Y5A11
Ignition system
In order to determine the optimal ignition timing that is necessary for the proper operation of the
engine, the built-in microcomputer in the CDI unit detects the signals from various types of sensors
and controls the ignition timing in accordance with a control map that is based on those signals. The
microcomputer also effects controls to protect the engine against overheating, over-revolution, and
oil pressure drops, as well as to control warning devices.
1Pulser coil
2Flywheel
3Charge coil
4CDI unit
5Microcomputer
6Ignition coils #1 and #4
7Ignition coils #2 and #3
8Oil pressure switch
9Thermoswitch
Flywheel
Three protrusions for the pulser coil are provided along the periphery of the flywheel. The purpose
of these protrusions is for detecting the engine speed. Two of them are used for ignition signals, and
one is used for identifying the cylinders, and these signals are transmitted to the microcomputer.
1
3
4
5
6
7
8
9
2
S62Y1310