Yamaha YZ125(R)/LC, Owner'S Service Manual

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7-10
TUN
SETTING
EC71C020
Road condition and examples of carburetor setting
EC71D040
Examples of carburetor setting depending on symptom
Symptom Setting Checking
At full throttle Increase main jet calibration No. Discoloration of spark plug
→
Stall at high speeds (Gradually) If tan color, it is in good condition.
*Hard breathing If can not be normalized:
Shearing noise Clogged float valve seat
Whitish spark plug Clogged fuel hose
Clogged fuel cock
Lean mixture
At full-throttle Decrease main jet calibration No. Discoloration of spark plug
→
Stop of speed pick-up (Gradually) If tan color, it is in good condition.
Slow speed pick-up *In case of racing slight enrichment If not effect:
of mixture reduces engine trouble. Clogged air cleaner
Slow response Fuel overflow from carburetor
Sooty spark plug Clogged main air passage or clogged
filter
Rich mixture
Lean mixture Lower jet needle clip position.
(1 groove down)
Rich mixture Raise jet needle clip position.
(1 groove up)
1/4~3/4 throttle Lower jet needle clip position.
*Hard breathing (1 groove down)
Lack of speed
1/4~1/2 throttle Raise jet needle clip position.
Slow speed pick-up (1 groove up)
White smoke
Poor acceleration
Conditions General condition Sandy condition
Under 10°C 15~25°C Over 30°C Under 10°C 15~25°C Over 30°C
(50°F) (59~77°F) (86°F) (50°F) (59~77°F) (86°F)
Parts (Winter) (Spring, Autumn) (Summer) (Winter) (Spring, Autumn) (Summer)
Main jet #420 #410 #400 #440 #430 #420
Jet needle
6CHY6-81-3 6CHY6-82-3 6CHY5-82-3 6CHY5-81-4 6CHY5-82-4 6CHY6-82-3
*6CHY6-81-4 *6CHY6-82-4 *6CHY5-82-4 *6CHY5-81-5 *6CHY5-82-5 *6CHY6-82-4
Pilot jet #40 #40 #40 #40 #40 #40
Pilot air screw
1-1/2
2 2
1-1/2
2 2
*1-1/2 *1-1/2 *1-1/2 *1-1/2
Leaner
(Standard)
Richer
→
→
Clip position indicates the position of jet
needle groove, to which the clip is fitted.
The position is numbered from the top.
If a change in the clip position (1
groove) is effective, try another jet nee-
dle that provides a difference of 0.5 in
the clip position.
*For EUROPE