Yamaha MZ250 2012 Manual

MZ250
MZ300
SUPPLEMENTARY
SERVICE MANUAL
7VB-F8197-11LIT-19616-01-88
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FOREWORD
This Supplementary Service Manual has been
prepared to introduce new service and new
data for the MZ250 and MZ300.
For complete information on service proce-
dures, it is necessary to use this Supplementary
Service Manual together with following manual:
This Manual Was Written By The Yamaha
Motor Powered Products Co., Ltd. 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 per-
form maintenance and repairs on Yamaha
Multi-Purpose Engine have a basic under-
standing of the mechanical precepts and pro-
cedures inherent to Multi-Purpose Engine
repair technology. Without such knowledge,
attempted repairs or service to this model may
render it unfit for use and/or unsafe.
Yamaha Motor Powered Products Co., Ltd. is
continually striving to further improve all mod-
els 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.
HOW TO USE THIS MANUAL
PARTICULARLY IMPORTANT
INFORMATION
Particularly important information is distin-
guished in this manual by the following nota-
tions.
This is the safety alert symbol. It is used to
alert you to potential personal injury haz-
ards. Obey all safety messages that follow
this symbol to avoid possible injury or
death.
WARNING
A WARNING indicates a hazardous situa-
tion which, if not avoided, could result in
death or serious injury.
NOTICE
A NOTICE indicates special precautions
that must be taken to avoid damage to the
machine or other property.
TIP
A TIP provides key information to make proce-
dures easier or clearer.
MZ250/MZ300
SUPPLEMENTARY SERVICE MANUAL
©2012 by Yamaha Motor
Corporation, U.S.A.
1st Edition, September 2012
All rights reserved. Any reprinting or
unauthorized use without the written
permission of Yamaha Motor
Corporation, U.S.A.
is expressly prohibited.
LIT-19616-01-88
MZ250/MZ300
SERVICE MANUAL:
7VB-F8197-10. LIT-19616-01-80

HOW TO USE THIS MANUAL
This manual is intended as a handy, easy-to-read reference book for the mechanic.
Comprehensive explanations of all installation, removal, disassembly, assembly, repair and check
procedures are laid out with the individual steps in sequential order.
9 The manual is divided into chapters and each chapter is divided into sections. The current sec-
tion title is shown at the top of each page 1.
9 Sub-section titles appear in smaller print than the section title 2.
9 To help identify parts and clarify procedure steps, there are exploded diagrams at the start of
each removal and disassembly section 3.
9 Numbers are given in the order of the jobs in the exploded diagram. A number indicates a dis-
assembly step 4.
9 Symbols indicate parts to be lubricated or replaced 5.
Refer to “ILLUSTRATED SYMBOLS”.
9 A job instruction chart accompanies the exploded diagram, providing the order of jobs, names of
parts, notes in jobs, etc. 6.
9 Jobs requiring more information (such as special tools and technical data) are described
sequentially 7.
3-21
ENG
CYLINDER HEAD COVER, CYLINDER HEAD
12 Nm (1.2 m · kgf, 8.7 ft · lbf)
50 Nm (5.0 m · kgf, 36 ft · lbf)
1st
2nd
6
5
4
3
1
2
78
9
9
78
7 Nm (0.7 m · kgf, 5.1 ft · lbf)
11 Nm (1.1m · kgf, 8.0 ft · lbf)
11 Nm (1.1m · kgf, 8.0 ft · lbf)
20 Nm (2.0 m · kgf, 14 ft · lbf)
2.3 Nm (0.23m · kgf, 1.7 ft · lbf)
Order Job/Parts to remove Q’ty Remarks
Removing the cylinder head cover
and cylinder head
Remove the parts in the order listed
below.
Fuel tank Refer to “FUEL TANK, CANISTER” on 3-5.
Muffler Refer to “MUFFLER” on 3-7.
Air filter Refer to “AIR FILTER” on 3-3.
Carburetor Refer to “CARBURETOR” on 4-1.
Flywheel cover Refer to “FLYWHEEL” on 3-13.
1 Spark plug cap 1
2 Spark plug 1
3 Breather hose 1
4 Cylinder head cover 1
5 Cylinder head cover gasket 1
6 Cylinder air shroud 1
7 Locknut 2
8 Adjuster 2
9 Screw 2
CYLINDER HEAD COVER, CYLINDER HEAD
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3-23
ENG
CYLINDER HEAD COVER, CYLINDER HEAD
CHECKING THE PUSH ROD
1. Check:
9 Push rod runout
Runout limit:
Refer to “SPECIFICATIONS” in
the Supplementary service
manual.
Out of specifications → Replace.
CHECKING THE CYLINDER HEAD
1. Check:
9 Cylinder head combustion chamber
Check the combustion chamber for car-
bon deposits.
Any carbon deposits → Eliminate.
TIP
Be sure not to damage the contact surface of
the cylinder.
2. Check:
9 Cylinder head
Cracks/damage around the hole of
spark plug → Replace.
CHECKING THE ROCKER ARM
1. Check:
9 Rocker arm
Wear/damage/cracks → Replace.
chap03.indd 23 2012/09/14 10:45:52
1
4
3
6
7
2
5

ILLUSTRATED SYMBOLS
(Refer to the illustration)
SYMBOL DEFINITION SYMBOL DEFINITION
General information Periodic checks and
adjustments
Engine Carburetor
Electrical Troubleshooting
Specifications Filling fluid
Lubricant Special tool
T
R
.
.
Tightening torque Wear limit, clearance
Engine speed Electrical data
Replace the part with a new one. LS Lithium-soap base grease
MMolybdenum disulfide grease
E
Engine oil
M
Molybdenum disulfide oil LT Apply locking agent (LOCTITE®)

INDEX
GENERAL INFORMATION GEN
INFO
ENGINE ENG
ELECTRICAL
ELEC
SPECIFICATIONS SPEC
1
2
3
4

CHAPTER 1.
GENERAL INFORMATION
MACHINE IDENTIFICATION .....................1-1
ENGINE SERIAL NUMBER ..................1-1
STARTING SERIAL NUMBER ..............1-1
DIMENSIONS .............................................1-2
DIMENSION CHART ............................1-2
TOP (MZ250A/MZ300A) .......................1-3
LEFT SIDE (MZ250A/MZ300A) ............1-3
RIGHT SIDE (MZ250A/MZ300A) ..........1-4
FRONT (MZ250A/MZ300A) ..................1-5
MOUNTING BASE
(MZ250A/MZ300A) ...............................1-5
TOP (MZ250K/MZ300K) .......................1-6
LEFT SIDE (MZ250K/MZ300K) ............1-6
RIGHT SIDE (MZ250K/MZ300K) ..........1-7
FRONT (MZ250K/MZ300K) ..................1-8
MOUNTING BASE
(MZ250K/MZ300K) ...............................1-8
CHAPTER 2.
ENGINE
GOVERNOR ...............................................2-1
MZ250A/MZ300A ..................................2-1
MZ250K ................................................2-2
MZ300K ................................................2-3
ADJUSTING THE GOVERNOR ............2-4
CHAPTER 3.
ELECTRICAL
CIRCUIT DIAGRAM ...................................3-1
MZ250/MZ300 .......................................3-1
CHAPTER 4.
SPECIFICATIONS
GENERAL SPECIFICATIONS ...................4-1
MAINTENANCE SPECIFICATIONS ..........4-3
ENGINE ................................................4-3
ELECTRICAL ........................................4-7
TIGHTENING TORQUES ...........................4-8
GENERAL TORQUE
SPECIFICATIONS ....................................4-10
LUBRICATION POINTS AND TYPE
OF LUBRICANTS ....................................4-11
WIRE ROUTING DIAGRAM ....................4-12
UPPER SIDE VIEW ............................4-12
ENGINE SWITCH AND OIL
WARNING UNIT .................................4-13
TCI UNIT AND CHARGING COIL ......4-14
OIL LEVEL SWITCH
(CRANKCASE COVER) .....................4-15
UPPER SIDE VIEW
(MZ250KHID0/MZ300KHID3) .............4-16
UPPER SIDE VIEW
(MZ300KHIDM) ...................................4-17
CARBURETOR AND CHARGING
COIL (MZ300KHIDM) .........................4-18

1-1
GEN
INFO
MACHINE IDENTIFICATION
1
1
2
GENERAL INFORMATION
MACHINE IDENTIFICATION
ENGINE SERIAL NUMBER
The serial number is printed on the label 1
affixed to the position 2 of the multi-purpose
engine as shown in the illustration.
TIP
The first three digits identify the model, and
the remaining digits indicates the production
number.
STARTING SERIAL NUMBER
Model Code Starting serial
number
MZ250AAIA0 7KBJ 7KBJ-1000101–
MZ250KHID0 7KBN 7KBN-1000101–
MZ300AAIA0 7VBJ 7VBJ-1000101–
MZ300KHID3 7VBN 7VBN-1000101–
MZ300KHIDM 7VBN 7VBN-2000101–
TIP
Designs and specifications are subject to
change without notice.

1-2
GEN
INFO
DIMENSIONS
DIMENSIONS
DIMENSION CHART
Unit: mm
Model (Code) PTO shaft dimensions (Type) Mounting face dimensions
MZ250 AAIA0
(7KBJ)
94.5
å
7/16 -20UNF-2B
4.5
5
28
72.2
56
88.5
25.4 -0.021
0
110 +0.054
0
146.08 -0.040
0
21.8 -0.1
0
6.31
30
30
146.08
0
-0.040
45
45
165.1
127
110 +0.054
0
4 M8 1.25DEPTH18
43/8 -16UNC2BDEPTH18
45
45
MZ300 AAIA0
(7VBJ)
MZ250 KHID0
(7KBN)
94.5
110 +0.054
0
22.161 -0.021
0
25.4 -0.021
0
146.08 -0.040
0
18
46.8 58.7
4.5
5
29.5 76
5/16 -24UNF-2B
3/16
∫
å
4 M8 1.25DEPTH18
4
127
146.08
165.1
30
30
45
0
-0.040
45
45
45
3/8 -16UNC2BDEPTH18
110 +0.054
0
MZ300 KHID3
(7VBN)
MZ300 KHIDM
(7VBN)
*1: UNF; Unified fine thread (Unit: in)
*2: UNC; Unified coarse thread (Unit: in)
A To Engine center
B Taper

1-3
GEN
INFO
DIMENSIONS
TOP (MZ250A/MZ300A)
Unit: in (mm)
LEFT SIDE (MZ250A/MZ300A)
Unit: in (mm)
1.38
(35)
1.38
(35)
4 M8 0.05 (1.25) DEPTH 0.71 (18)
4.06 (103)
16.77 (426)

1-4
GEN
INFO
DIMENSIONS
RIGHT SIDE (MZ250A/MZ300A)
Unit: in (mm)
5.26 (133.5)
18.27 (464)
4.13 (105) 3.56 (90.5)

1-5
GEN
INFO
DIMENSIONS
FRONT (MZ250A/MZ300A)
Unit: in (mm)
cm3
ON
OFF
15.24 (387)
7.20 (183)
3.50 (89)
0.83
(21)
2.26
(57.5)
2.32
(59)
1.46
(37)
2 0.43 (11) 1.06 (27) (SLOT HOLE)
2 0.43 (11) (HOLE)
MOUNTING BASE (MZ250A/MZ300A)
Unit: in (mm)
2
0.43 (11)
4.13 (105)
3.56 (90.5)
2 0.43 (11)
2.32 (59)
1.46
(37)
4
R
0.63 (16)

1-6
GEN
INFO
DIMENSIONS
TOP (MZ250K/MZ300K)
Unit: in (mm)
LEFT SIDE (MZ250K/MZ300K)
Unit: in (mm)
10.91 (277)
5.75 (146)
1.38
(35)
1.38
(35)
4 M8 0.05 (1.25) DEPTH 0.71 (18)
5.61 (142.5)
7.09 (180)
10.63 (270)
7.09 (180.2)
4.06 (103)
15.91 (404)

1-7
GEN
INFO
DIMENSIONS
RIGHT SIDE (MZ250K/MZ300K)
Unit: in (mm)
5.26 (133.5) 6.34 (161)

1-8
GEN
INFO
DIMENSIONS
FRONT (MZ250K/MZ300K)
Unit: in (mm)
cm
3
ON
OFF
15.91 (404)
7.87 (200)
4.15 (105.5)
0.83
(21)
2.26
(57.5)
2.32
(59)
1.46
(37)
2 0.43 (11) 1.06 (27) (SLOT HOLE)
2 0.43 (11) (HOLE)
MOUNTING BASE (MZ250K/MZ300K)
Unit: in (mm)
2
0.43 (11)
4.13 (105)
3.56 (90.5)
2 0.43 (11)
2.32 (59)
1.46
(37)
4
R
0.63 (16)

2-1
ENG
GOVERNOR
8 Nm (0.8 m · kgf, 5.8 ft · lbf)
7 Nm (0.7 m · kgf, 5.1 ft · lbf)
3
4
2
1
5
1.1 Nm (0.11 m · kgf, 0.80 ft · lbf)
Order Job/Parts to remove Q’ty Remarks
Removing the governor Remove the parts in the order listed.
Fuel tank Refer to “FUEL TANK, CANISTER” in
7VB-F8197-10 chapter 3.
Fuel tank stay Refer to “FUEL TANK, CANISTER” in
7VB-F8197-10 chapter 3.
Engine switch and oil warning unit
Refer to “ENGINE SWITCH AND OIL
WARNING UNIT” in 7VB-F8197-10 chapter 3.
1 Link rod 1
2 Spring 1
3 Spring 1
4 Governor arm 1
5 Throttle lever assembly 1
For installation, reverse the removal pro-
cedure.
ENGINE
GOVERNOR
MZ250A/MZ300A
2

2-2
ENG
GOVERNOR
8 Nm (0.8 m · kgf, 5.8 ft · lbf)
7 Nm (0.7 m · kgf, 5.1 ft · lbf)
2
1
4
3
5
Order Job/Parts to remove Q’ty Remarks
Removing the governor Remove the parts in the order listed.
Engine switch and oil warning unit Refer to “ENGINE SWITCH AND OIL
WARNING UNIT” in 7VB-F8197-10
chapter 3.
1 Link rod 1
2 Spring 1
3 Spring 1
4 Governor arm 1
5 Adjusting plate assembly 1
For installation, reverse the removal pro-
cedure.
MZ250K

2-3
ENG
GOVERNOR
8 Nm (0.8 m · kgf, 5.8 ft · lbf)
5
3
4
2
1
16 Nm (1.6 m · kgf, 12 ft · lbf)
7 Nm (0.7 m · kgf, 5.1 ft · lbf)
Order Job/Parts to remove Q’ty Remarks
Removing the governor Remove the parts in the order listed.
Engine switch and oil warning unit Refer to “ENGINE SWITCH AND OIL
WARNING UNIT” in 7VB-F8197-10
chapter 3.
1 Link rod 1
2 Spring 1
3 Spring 1
4 Governor arm 1
5 Adjusting plate assembly 1
For installation, reverse the removal pro-
cedure.
MZ300K

2-4
ENG
GOVERNOR
3
2
1
ADJUSTING THE GOVERNOR
1. Remove:
9 Fuel tank
(Refer to “FUEL TANK, CANISTER” in
7VB-F8197-10 chapter 3.)
2. Adjust:
9 Governor
Adjustment steps:
a. Loosen the governor arm bolt 1.
b. Turn the governor arm 2 clockwise
until it stops.
c. Turn the governor shaft 3 clockwise
until it stops.
d. Tighten the governor arm bolt 1.
8 Nm (0.8 m · kgf, 5.8 ft · lbf)