Relationship With Throttle Opening; Carburetor Setting Parts - Yamaha YZ250 Owner's Service Manual

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>
N3EW-3
N3EW-4
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

Main jet
"1"
Rich #190
*(STD) #180
(STD) #178
Lean #162
Pilot jet
"2"
Rich
* (STD)
(STD)
N3EJ-3
N8RW-3
Lean
* Except for USA and CDN
Part number
Size
(-14943-)
4MX-45
#188 4MX-95
#185 4MX-44
#182 4MX-94
4MX-43
4MX-93
#175 4MX-42
#172 4MX-92
#170 4MX-41
#168 4MX-91
#165 4MX-40
4MX-90
Part number
Size
(-14948-)
#62 4MX-12
#60 4MX-11
#58 4MX-10
#55 4MX-09
#52 4MX-08
#50 4MX-07
#48 4MX-06
#45 4MX-05
#42 4MX-04
#40 4MX-03
#38 4MX-02
7-3
ENGINE
Jet nee-
Size
dle "3"
Rich N8RH
N3EH
N8RW
(STD) N3EW
N3CW
N3EJ
Lean N3CJ
Power jet
Size
"4"
Rich #65
#60
#55
(STD) #50
Lean #40
Part
number
(-14916-)
4SR-RH
4SR-EH
4SR-RW
4SR-EW
4SR-CW
4SR-EJ
4SR-CJ
Part
number
(-1494F-)
4JT-13
4JT-11
4JT-09
4JT-07
4JT-03