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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 symptom
Conditions
Parts
General 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 mixture
Increase 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 mixture
Decrease 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 speed
Use 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 acceleration
Use jet needle with a larger diam-
eter, or NBKG.
Raise jet needle clip position.
Closed to 1/4 throttle
*Hard breathing
Speed down
Use jet needle with a smaller
diameter.
Turn out pilot air screw.
Leaner
↑
(Standard)
↓
Richer
SETTING
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