Service manual

TUN
9-5
ROAD CONDITION AND EXAMPLES OF CARBURETOR SETTING
N
O
TE:
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
Diameter of straight portion
Clip position
Rich Lean
φ 2.405 mm (0.0947 in) φ 2.415 mm (0.0951 in) φ 2.425 mm (0.0955 in)
Rich 1 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
Lean 1 leaner NBKE-1st groove NBKF-1st groove NBKG-1st groove
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 enrichment of mix-
ture 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.
Rich mixture Use jet needle with a larger diameter, 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 diameter, or
NBKG.
Raise jet needle clip position.
The clip position is the jet needle groove
on which the clip is installed. The positions
are numbered from the top.
Closed to 1 / 4 throttle
*Hard breathing
Speed down
Use jet needle with a smaller diameter.
Turn out pilot air screw.
Leaner
Clip
Jet needle
Groove 1
Groove 2
Groove 3
Groove 4
Groove 5
(Standard)
Richer
ENGINE