Yamaha Wr 450 F Owners Manual

 
7 - 3
TUN
 
SETTING 
Effects of the setting parts on the throttle 
valve opening 
1  
Pilot screw/pilot jet  
2  
Throttle valve cutaway  
3  
Jet needle  
4  
Main jet
ÅClosed
ıFully open
1/2 3/4 1/4 1/8
1
2
3
4
Åı  
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. Use the main jet and the
jet needle to set the carburetor.
 
1  
Jet needle  
2  
Pilot air jet  
3  
Needle jet...

 
7 - 4
TUN
 
SETTING 
Pilot system 
The FLATCR carburetor is manufactured with
a pilot screw. The pilot screw adjustment
ranges from fully closed throttle to 1/4 open
throttle. 
Main jet adjustment 
The richness of the air-fuel mixture at full throt-
tle can be set by changing the main jet  
1  
.
* Except for USA
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) 
Å 
Idle 
ı  
Fully open 
Standard...

 
7 - 5
TUN
 
SETTING 
Pilot screw adjustment 
The richness of the air-fuel mixture with the
throttle fully closed to 1/4 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:
 
 
If the idling speed fluctuates, turn the pilot
screw only 1/2 of a turn in either direction. 
 
To optimize the fuel flow at a smaller throttle
opening, each machine’s pilot screw has
been individually...

 
7 - 6
TUN
 
SETTING 
Pilot jet adjustment 
The richness of the air-fuel mixture with the
throttle open 1/4 or less can be set by adjust-
ing the pilot jet  
1 
.
* Except for USA 
Effects of adjusting the pilot jet (reference) 
Å 
Idle 
ı 
Fully open 
Jet needle groove position adjustment 
Adjusting the jet needle  
1 
 position affects the
acceleration when the throttle is 1/8 to 3/4
open.
1. Too rich at intermediate speeds
Rough engine operation is felt and the
engine will not pick up speed smoothly....

7 - 7
TUN
Jet needle adjustment
The jet needle is adjusted by changing it.
* Except for USA
The tapered sections of all jet needles have
the same starting positions, but the needles
are available with different straight-portion
diameters.Standard jet needleOBDUT
*OBDUQ

OBDUT - 4
Clip position
Diameter a of straight portion
Effects of changing the jet needle 
(reference)
(Diameter of the straight portion)
Changing the diameter of the straight portion
adjusts the air-fuel mixture when the throttle is
1/8...

7 - 8
TUNSETTING
Carburetor setting parts
* Except for USAPart name Size Part number
Main jet  Rich
*(STD)
(STD)
Lean#170
#168
#165
#162
#160
#158
#155
#152
#150
#148
#145
#142
#1404MX-14943-41
4MX-14943-91
4MX-14943-40
4MX-14943-90
4MX-14943-39
4MX-14943-89
4MX-14943-38
4MX-14943-88
4MX-14943-37
4MX-14943-87
4MX-14943-36
4MX-14943-86
4MX-14943-35
Pilot jet Rich
*(STD)
(STD)
Lean#52
#50
#48
#45
#42
#404MX-14948-08
4MX-14948-07
4MX-14948-06
4MX-14948-05
4MX-14948-04
4MX-14948-03
Jet needle  Rich
(STD)...

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TUN
Examples of carburetor setting depending on symptom
This should be taken simply for an example. It is necessary to set the carburetor while checking
the operating conditions of the engine.
Symptom Setting Checking
At full throttle
Hard breathing
Shearing noise
Whitish spark plug
Lean mixtureIncrease main jet calibration no.
(Gradually)Discoloration of spark plug → 
If tan color, it is in good condition.
If cannot be corrected:
Clogged float valve seat
Clogged fuel hose
Clogged fuel cock
Check...

7 - 10
TUN
EC720000
CHASSIS
EC71P002
Selection of the secondary reduction ratio
(Sprocket)
Secondary 
reduction = 
ratio

It is generally said that the secondary gear
ratio should be reduced for a longer straight
portion of a speed course and should be
increased for a course with many corners.
Actually, however, as the speed depends on
the ground condition of the day of the race,
be sure to run through the circuit to set the
machine suitable for the entire course.
In actuality, it is very difficult to...

7 - 11
TUNSETTING
EC72N000
Drive and driven sprockets setting parts
* For CDN, EUROPE, AUS, NZ and ZA
* For AUS and NZPart name Size Part number
Drive sprocket 1 
(STD)
*(STD)14T
*14T5NG-17460-00
9383E-14215
Part name Size Part number
Driven sprocket 2 
(STD)
*(STD)48T
*48T
*49T
50T
*50T
*51T
52T
*52T5GS-25448-50
5NY-25448-00
5NY-25449-00
5GS-25450-50
5NY-25450-00
5NY-25451-00
5GS-25452-50
5NY-25452-00
EC721002
Tire pressure
Tire pressure should be adjust to suit the road
surface condition of the...

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TUNSETTING
EC722011
Front fork setting
The front fork setting should be made depend-
ing on the rider’s feeling of an actual run and
the circuit conditions.
The front fork setting includes the following
three factors:
1. Setting of air spring characteristics
Change the fork oil level.
2. Setting of spring preload
Change the spring.
Install the adjustment washer.
3. Setting of damping force
Change the compression damping.
Change the rebound damping.
The spring acts on the load and the
damping...