Yamaha yz250 2015, Owner'S Manual

Page: 165 / 174

7-3
ENGINE
RELATIONSHIP WITH THROTTLE
OPENING
The flow of the fuel through the car-
buretor main system is controlled by
the main jet and then, it is further reg-
ulated by the area between the main
nozzle and the jet needle. On the re-
lationship between the fuel flow and
the throttle opening, the fuel flow re-
lates to the jet needle straight portion
diameter around 1/8 to 1/4 throttle
opening, whereas around 1/4 to 1/1
throttle opening it relates to the taper
starting position and to the clip posi-
tion.
Therefore, the fuel flow is balanced at
each stage of throttle opening by the
combination of the jet needle straight
portion diameter, taper starting posi-
tion and clip position.
<Example>
A. Lean (larger diameter)
B. Rich (smaller diameter)
1. 1/8 throttle
2. 1/4 throttle
3. 1/2 throttle
4. 1/1 throttle
a. Main nozzle
CARBURETOR SETTING PARTS
N3EW-3
N3EW-4
N3EJ-3
N8RW-3
Main jet
"1"
Size
Part number
(-14943-)
Rich #190 4MX-45
#188 4MX-95
#185 4MX-44
#182 4MX-94
*(STD) #180 4MX-43
(STD) #178 4MX-93
#175 4MX-42
#172 4MX-92
#170 4MX-41
#168 4MX-91
#165 4MX-40
Lean #162 4MX-90
Pilot jet
"2"
Size
Part number
(-14948-)
Rich #62 4MX-12
#60 4MX-11
#58 4MX-10
#55 4MX-09
* (STD) #52 4MX-08
(STD) #50 4MX-07
#48 4MX-06
#45 4MX-05
#42 4MX-04
#40 4MX-03
Lean #38 4MX-02
* Except for USA and CDN
Jet nee-
dle "3"
Size
Part
number
(-14916-)
Rich N8RH 4SR-RH
N3EH 4SR-EH
N8RW 4SR-RW
(STD) N3EW 4SR-EW
N3CW 4SR-CW
N3EJ 4SR-EJ
Lean N3CJ 4SR-CJ
Power jet
"4"
Size
Part
number
(-1494F-)
Rich #65 4JT-13
#60 4JT-11
#55 4JT-09
(STD) #50 4JT-07
Lean #40 4JT-03