fuel YAMAHA YZ426F 2000 Owner's Guide

ENG
4 - 67
CDI MAGNETO
EC4L0000
CDI MAGNETO
Extent of removal:1 CDI magneto removal
Extent of removal Order Part name Q’ty Remarks
CDI MAGNETO REMOVAL
Preparation for removal Seat and fuel tankRefer to “SAET, FUEL TANK AND SIDE
COVERS” section.
Bolt [radiator (left)]
Disconnect the CDI magneto lead.Refer to “RADIATOR” section.
1 Shift pedal 1
2 Crankcase cover (left) 1
3 Gasket 1
4 Dowel pin 2
5 Nut (rotor) 1 Use special tool.
Refer to “REMOVAL POINTS”.
6 Rotor 1
7 Stator 1
8 Woodruff key 1
1

ENG
4 - 71
ENGINE REMOVAL
EC4M0000
ENGINE REMOVAL
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for removal Hold the machine by placing the
suitable stand under the frame.
Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Clutch cable Disconnect at engine side.
Decompression cable and guide Disconnect at engine side.
Radiator Refer to “RADIATOR” section.
Shift pedal Refer to “CDI MAGNETO” section.
Cylinder head breather hose and
oil tank breather hoseRefer to “CAMSHAFTS” section.
Drain the engine oil Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Spark plug cap
Disconnect the CDI magneto lead.
WARNING
Support the machine securely so there is nodanger of it falling over.

5 - 44
CHASHANDLEBAR
NOTE:
lThe “ENGINE STOP” button, clutch lever
holder and clamp should be installed accord-
ing to the dimensions shown.
lPass the “ENGINE STOP” button lead in the
middle of the clutch holder.
8. Install:
lClutch cable 1
NOTE:
Apply the lithium soap base grease on the
clutch cable end.
9. Adjust:
lClutch lever free play
Refer to “CLUTCH ADJUSTMENT”
section in the CHAPTER 3.
10. Clamp the clamp portion a of the num-
ber plate to the handlebar.
11. Insert the end of the fuel breather hose
1 into the hole of the number plate.

5 - 57
CHASREAR SHOCK ABSORBER
EC580000
REAR SHOCK ABSORBER
Extent of removal:1 Rear shock absorber removal2 Rear shock absorber disassembly
Extent of removal Order Part name Q’ty Remarks
Preparation for removalREAR SHOCK ABSORBER
REMOVAL
Hold the machine by placing the
suitable stand under the engine.
Seat and fitting band Refer to “SAET, FUEL TANK AND SIDE
COVERS” section.
Silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
1 Bolt (reservoir tank) 1
2 Clamp (air cleaner joint) 1Only loosening.
3 Rear frame 1
4 Bolt (rear shock absorber-relay
arm)1 Hold the swingarm.
5 Bolt (rear shock absorber-frame) 1
6 Rear shock absorber 1
7 Locknut 1Only loosening.
8 Adjuster 1Only loosening.
9 Spring guide (lower) 1
WARNING
Support the machine securely so there is nodanger of it falling over.
1
2

6 - 3
–+ELEC

IGNITION SYSTEM
EC620000
IGNITION SYSTEM
EC621001
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
*marked: Only when the ignition checker is used.
NOTE:

l
Remove the following parts before inspection.
1) Seat
2) Fuel tank
l
Use the following special tools in this inspection.
Spark gap test*Clean or replace
spark plug.
Check entire ignition
system for connection.Repair or replace.
Check “ENGINE STOP”
button.Replace.
Check ignition coil. Primary coil Replace.
Secondary coilReplace.
Check CDI magneto. Pick-up coil Replace.
Source coil Replace.
Check neutral switch. Repair or replace.
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754
Pocket tester:
YU-03112/90890-03112
No Spark
OK
OK
OK
OK
Spark
No good
No good
No good
No good
No good
No good
No good
OK

6 - 7
–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
EC69000
TPS (THROTTLE POSITION SENSOR) SYSTEM
EC691000
INSPECTION STEPS
If the TPS will not operate, use the following inspection steps.
*marked: Refer to “IGNITION SYSTEM” section.
NOTE:
lRemove the following parts before inspection.
1) Seat
2) Fuel tank
lUse the following special tools in this inspection.
Check entire ignition
system for connection.Repair or replace.
Check TPS. TPS coil Replace.
*Check CDI magneto. Source coil Replace.
Check CDI unit.TPS input
voltageReplace.
Pocket tester:
YU-03112/90890-03112Inductive tachometer:
YU-8036-1
Engine tachometer:
90890-03113
No good
No good
No good
No good
OK
OK
OK

7 - 1
TUN

EC700000
TUNING
EC710000
ENGINE
Carburetor setting
l
The air/fuel mixture will vary depending on
atmospheric conditions. Therefore, it is nec-
essary to take into consideration the air pres-
sure, ambient temperature, humidity, etc.,
when adjusting the carburetor.
l
Perform a test run to check for proper engine
performance (e.g., throttle response) and
spark plug(-s) discoloration or fouling. Use
these readings to determine the best possi-
ble carburetor setting.
NOTE:

It is recommended to keep a record of all car-
buretor settings and external conditions (e.g.,
atmospheric conditions, track/surface condi-
tions, lap times) to make future carburetor set-
ting easier.
WARNING

l
The carburetor is a part of the fuel line.
Therefore, be sure to install it in a well-
ventilated area, away from flammable
objects and any sources of fire.
l
Never look into the carburetor intake.
Flames may shoot out from the pipe if the
engine backfires while it is being started.
Gasoline may be discharged from the
accelerator pump nozzle when the carbu-
retor has been removed.
CAUTION:

l
The carburetor is extremely sensitive to
foreign matter (dirt, sand, water, etc.).
During installation, do not allow foreign
matter to get into the carburetor.
l
Always handle the carburetor and its com-
ponents carefully. Even slight scratches,
bends or damage to carburetor parts may
prevent the carburetor from functioning
correctly. Carefully perform all servicing
with the appropriate tools and without
applying excessive force.
l
When the engine is stopped or when
riding at no load, do not open and close
the throttle unnecessarily. Otherwise, too
much fuel may be discharged, starting
may become difficult or the engine may
not run well.
SETTING
7

7 - 2
TUN

l
After installing the carburetor, check that
the throttle operates correctly and opens
and closes smoothly.
Atmospheric conditions and carburetor
settings
The air density (i.e., concentration of oxygen
in the air) determines the richness or lean-
ness of the air/fuel mixture. Therefore, refer
to the above table for mixture settings.
That is:
l
Higher temperature expands the air with its
resultant reduced density.
l
Higher humidity reduces the amount of oxy-
gen in the air by so much of the water vapor
in the same air.
l
Lower atmospheric pressure (at a high alti-
tude) reduces the density of the air.
Air temp. HumidityAir
pressure
(altitude)Mixture Setting
High High Low (high) Richer Leaner
Low Low High (low) Leaner Richer
SETTING
Effects of the setting parts on the throttle
valve opening

Closed
õ
Fully open
4/4
3/4
1/2
1/4
1/8
0õ


1/2 3/4 1/4 1/8
AB
1
2
3
4
1
Pilot screw/pilot jet
2
Piston valve cutaway
3
Jet needle
4
Main jet

7 - 3
TUN

SETTING
Main system
The FLATCR carburetor has a primary main
jet. This type of main jet is perfect for racing
motorcycles since it supplies an even flow of
fuel, even at full load. The main air jet has
almost no effect on the air-fuel mixture. Use
the main jet and the jet needle to set the car-
buretor.
1
Jet needle
2
Main air jet
3
Pilot air jet
4
Needle jet
5
Main jet
6
Pilot jet
7
Pilot screw
Pilot system
The FLATCR carburetor is manufactured with
a pilot screw. The adjusting range of the pilot
screw is limited by the throttle opening during
idling. Therefore, even a large adjustment of
the pilot screw will have no effect until the
throttle is 1/8 to 1/4 open.
To set the pilot system of the carburetor,
adjust the pilot jet and pilot air jet, while mak-
ing sure not to adjust one without adjusting the
other. Do not adjust the pilot screw.

7 - 4
TUN

SETTING
Main jet adjustment
The richness of the air-fuel mixture at full throt-
tle can be set by changing the main jet
1
.
If the air-fuel mixture is too rich or too lean, the
engine power will drop, resulting in poor accel-
eration.
Effects of changing the main jet (reference)

Idle
õ
Fully open
Standard main jet #162
1/4 1/2 3/4
+10%
#162
–10%
#172
#152
õ

Pilot screw adjustment
The richness of the air-fuel mixture with the
throttle fully closed to 1/8 open can be set by
turning the pilot screw
1
. Turning in the pilot
screw will make the mixture lean at low
speeds, and turning it out will enrich it.
* Except for USA
NOTE:

The pilot screw is set at the factory, there is no
need to adjust it.
If the idling speed fluctuates, turn the pilot
screw only 1/2 of a turn in either direction.
Effects of adjusting the pilot screw (refer-
ence)

Idle
õ
Fully open
1
2-1/4 turns out
2
1-1/4 turns out
3
1-3/4 turns out
Standard pilot
screw position1-3/4
* 1-1/2
(for reference only)
1/4 1/2 3/4
+5%
–5% AB
1
23