7 - 4
TUNSETTING
EC71R000
Pilot jet adjustment
The air-fuel mixture can basically be adjusted
by the pilot air screw from full closed to 1/2
throttle.
If the pilot air screw is not enough for this
adjustment, the pilot jet 1 is changed.
A larger size jet results in a richer mixture at
low speeds, and a smaller size in a leaner mix-
ture.
Standard pilot jet #45
5PA70070
Jet needle adjustment
The richness of air-fuel mixture with 1/4 ~ 3/4
throttle can be set by changing the jet needle
1.
A smaller diameter jet needle results in a richer
mixture at middle speeds, and a larger diame-
ter in a leaner mixture.
Standard jet needle NBKF
5PA70080
7 - 6
TUNSETTING
EC71Q000
Carburetor setting parts
Part name Size Part number
Main jet
1Rich
(STD)
Lean#148
#145
#142
#140
#138
#135
#1324MX-14943-87
4MX-14943-36
4MX-14943-86
4MX-14943-35
4MX-14943-85
4MX-14943-34
4MX-14943-84
Pilot jet
2Rich
(STD)
Lean#48
#45
#424MX-14948-06
4MX-14948-05
4MX-14948-04
Jet needle
3
Refer to the following
table about the
change in the air-fuel
mixture ratio due to a
different jet needle.
NBLE
NBLF
NBLG
NBKE
NBKF
NBKG5PA-14916-LE
5PA-14916-LF
5PA-14916-LG
5PA-14916-KE
5PA-14916-KF
5PA-14916-KG
Diameter of straight portion
Clip positionRich Lean
f 2.405 mm (0.0947 in)f 2.415 mm (0.0951 in)f 2.425 mm (0.0955 in)
Rich
Lean1 richer NBKE-3rd groove NBKF-3rd groove NBKG-3rd groove
0.5 richer NBLE-2nd groove NBLF-2nd groove NBLG-2nd groove
STD NBKE-2nd groove NBKF-2nd groove (STD) NBKG-2nd groove
0.5 leaner NBLE-1st groove NBLF-1st groove NBLG-1st groove
1 leaner NBKE-1st groove NBKF-1st groove NBKG-1st groove
5PA70100
7 - 7
TUN
Road condition and examples of carburetor setting
NOTE:
Optimum pilot air screw setting can be obtained by adding the ex-factory number of the same screw
back-out turns to any required value provided in the chart.
For example, if the ex-factory number is “2”, add “2” to the value chosen in the chart.
Examples of carburetor setting depending on symptomConditions
PartsGeneral condition Sandy condition
Under 10 °C
(50 °F)
(Winter)15 ~ 25 °C
(59 ~ 77 °F)
(Spring, Autumn)
Over 30 °C
(86 °F)
(Summer)Under 10 °C
(50 °F)
(Winter)15 ~ 25 °C
(59 ~ 77 °F)
(Spring, Autumn)
Over 30 °C
(86 °F)
(Summer)
Main jet #140 #138 #135 ~ #138 #142 #142 #142
Jet needle NBKF-2 NBKF-2 NBKF-2 NBKF-2 NBKF-2 NBKF-2
Pilot jet #45 #45 #45 #48 #48 #48
Pilot air screw Zero Zero +1/4 –1/2 –1/2 Zero ~ +1/2
Symptom Setting Checking
At full throttle
Stall at high speeds
*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
At full throttle
Speed pick-up stops
Slow speed pick-up
Slow response
Sooty spark plug
Rich mixtureDecrease main jet calibration no.
(Gradually)
*In case of racing slight enrich-
ment of mixture reduces engine
trouble.Discoloration of spark plug ®
If tan color, it is in good condition.
If cannot be corrected:
Clogged air filter
Fuel overflow from carburetor
Lean mixture Use jet needle with a smaller
diameter, or NBLF.
Lower jet needle clip position.
The clip position is the jet needle
groove on which the clip is
installed. The positions are num-
bered from the top. Rich mixture Use jet needle with a larger diam-
eter, or NBKG.
Raise jet needle clip position.
1/4 ~ 3/4 throttle
*Hard breathing
Lack of speedUse jet needle with a smaller
diameter, or NBLF.
Lower jet needle clip position.
1/4 ~ 1/2 throttle
Slow speed pick-up
White smoke
Poor accelerationUse jet needle with a larger diam-
eter, or NBKG.
Raise jet needle clip position.
Closed to 1/4 throttle
*Hard breathing
Speed downUse jet needle with a smaller
diameter.
Turn out pilot air screw.
Leaner
(Standard)
¯
Richer
SETTING
