Yamaha XT550J User manual

_YAMAHA
LIT-11616-03-00 5Y1-28197-10

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NOTICE
This manual was written by the Yamaha Motor Company primarily for use by Yamaha dealers
and their qualified mechanics. It is not possible to put an entire mechanic's education into one
manual, so it is assumed that persons using this book to perform maintenance and repairs on
Yamaha motorcycles have a basic understanding
of the mechanical concepts and procedures in-
herent
to motorcycle repair technology. Without such knowledge, attempted repairs or service
to this model may render it unfit to use and/ or unsafe.
This model
has been designed and manufactured to perform within certain specifications in
regard to performance and emissions. Proper service with the correct tools is necessary to en-
sure that the motorcycle will operate
as designed. If there is any question about a service pro-
cedure, it
is imperative that you contact a Yamaha dealer for any service information changes
that apply to this model. This policy is intended to provide the customer with the most satisfac-
tion from his motorcycle and
to conform with federal environmental qualityobjectives.
Yamaha Motor Company, Ltd.
is continually striving to improve all models manufactured by
Yamaha. Modifications and significant changes
in specifications or procedures will be forwarded
to all Authorized Yamaha dealers and will, where applicable, appear in future editions of this
manual.
NOTE:
______________________________________________________ __
This Service Manual contains information regarding periodic maintenance to the emission con-
trol system for the XT550J. Please read this material carefully.
Particularly important information is distinguished in this manual bythe following notations:
NOTE: A NOTE provides key information to make procedures easier or clearer.
CAU11ON: A CAUTION indicates special procedures that must be followed to avoid damage
to the motorcycle.
WARNING:
A WARNING indicates special procedures that must be followed to avoid injury
to a motorcycle operatoror person inspecting or repairing the motorcycle.
"
SERVICE DEPT.
INTERNATIONAL DIVISION
YAMAHA MOTOR CO., LTD.

GENERAL INFORMATION
PERIODIC INSPECTIONS
AND
ADJUSTMENTS
ENGINE OVERHAUL
CARBURETION
CHASSIS
ELECTRICAL
APPENDICES

CHAPTER·'. GENERAL INFORMATION
MOTORCYCLE IDENTIFiCATION ........ ........................ 1-1
A. Frame Serial Number .. . .... .. ............. . .................. 1-1
B. Engine Serial Number .......................... ... ....... ..... 1-1
C. Vehicle Identification Number . ..... . .................... . ...... 1-1
MAIN FEATURES. ............................................. 1-2
A. Dry Sump System and Monocross Suspension
............... . ..... 1-2
B. Four-Valve Engine ........................................... 1-3
C. Yamaha Duo Intake System (YDIS) ............... . .............. 1-4
D. Kick Synchronous Automatic Decompression ...................... 1-5
E. D. C. Lighting System ......................................... 1-6
F. Detachable Lighting System
.... . ... . ................ . ......... 1-7
G.
Fuel Tank Cap with Check Valve ................................ 1-8
SPECIAL TOOLS. .............................................. 1-9
A. For Tune-up .......... . ... ... ............ . .................. 1-9
B. For Engine Service ............ . .............................. 1-9
C. For Chassis Service ......... .. .............................. 1-12
D. For Electrical Components ..... . .............................. 1-12

GENERAL INFORMATION
MOTORCYCLE
IDENTIFICATION
A. Frame Serial Number
The frame serial number is stamped into the
right side
of the steering head pipe.
1. Frame Serial Number
Starting Serial Number:
XT550J .............. . ..... 5Y1-000101
B. Engine Serial Number
The engine serial number is stamped into the
elevated part of the right section of the
engine.
NOTE: ______________________ __
The first three digits of these numbers are for
model identification; the remaining digits are
the unit production number.
1-1
c. Vehicle Identification Number
The vehicle identification number is on the
left side of the steering head pipe.
1. Vehicle Identification Number

MAIN FEATURES
A. Dry Sump System and Monocross Suspension
The XT550J, which inherits the traditional XT500
dry sump system, features monoshock suspen-
sion, light weight, and a
new diamond-shaped
frame
with integrated oil tank.
1-2

B. Four-Valve Engine
Newly designed compact engine equipped with:
S.O.H.C., 4-Valve head, Dual intake and dual ex-
haust ports,gear-driven balancer,Yamaha Duo In-
take System (YDIS), and 5-speed transmission
1-3
\

C. Yamaha Duo Intake System (YOIS)
For this system, the primary carburetor and the secondary carburetor are equipped as a unit:
A cable-operated-slide type functions
as the primary carb, and a vaccum-controlled-slide type
provides asecondary bore. The engine has a4-valve head, and each carb
has its own intake port
and valve. Although each carb bore and intake port
is smaller than that of a more conventional
engine, their conbined area is about 20% greater than a single, larger carb and intake layout.
Flow efficiency
of both the intake and exhaust sides is substantially improved. From idle to about
half throttle, the primary carb supplies the air-fuel mixture, and almost the entire intake charge
enters through just one valve; since the 4-valve layout offsets the intake ports relative
to the
cylinder-bore axis, a strong YICS-type swirl is produced in the low-to-medium rpm range.
Combustion efficiency
is significantly enhanced, resulting in improved fuel economy. In addi-
tion, the single small bore provides excellent low- and medium-speed throttle response due to
the high air velocity in the venturi. This eliminates the need for a mechanical accelerator pump,
allowing minimal carb height and ample room for the Monocross rear suspension. As the throttle
is turned from half to wide open, a linkage between the carburetors gradually opens the
secondary-carb butterfly. The vaccum-controlled slide
in the secondary carb opens as engine
demand builds, providing superb mid-range smoothness. With both slides fully open, the engine
receives more mixture and produces more powerthan a regular single-carb machine.
SECONDARY
CARB
PRIMARY CARB
1-4
Top view
EXHAUST
INTAKE

D. Kick Synchronous Automatic Decompression
The kick-starting mechanism is interlinked with one of the exhaust valves, thus automatically
decompressing the combustion chamber for ease in kick-starting. Combined with electronic ad-
vance ignition, kick-starting is free from possible kickback. Correct adjustment is required of this
kick-synchronous automatic decompression system for effective performance.
1-5