Yamaha YZ125 2019 Owner's Service Manual page 225

ROAD CONDITION AND EXAMPLES OF CARBURETOR SETTING
Under 10°C
(50°F)
(Winter)
Main jet #440
Jet needle 6BFY44-74-
Pilot jet A #42.5
B #47.5
Pilot air screw 2-1/4
A. For USA and CAN
B. Except for USA and CAN
SPECIFICATIONS OF JET NEEDLE
Rich 1 richer
0.5 richer
STD
0.5 leaner
Lean 1 leaner
EXAMPLES OF CARBURETOR SETTING DEPENDING ON SYMPTOM
Symptom
At full throttle
Stall at high speeds
*Hard breathing
Shearing noise
Whitish spark plug
↓
Lean mixture
At full throttle
Stop of speed pick-up
Slow speed pick-up
Slow response
Sooty spark plug
↓
Rich mixture
General condition
15–25°C Over 30°C
(59–77°F)
(Spring, Au- (Summer)
tumn)
#430
6BFY43-74- 6BFY44-74-
3 3
#40
#45
2-1/4
ø2.72 mm ø2.73 mm
(0.1071 in) (0.1075 in)
6BFY43-72-4 6BFY43-73-4 6BFY43-74-4 6BFY43-75-4 6BFY43-76-4
6BFY44-72-3 6BFY44-73-3 6BFY44-74-3 6BFY44-75-3 6BFY44-76-3
6BFY42-72-4 6BFY42-73-4 6BFY42-74-4 6BFY42-75-4 6BFY42-76-4
6BFY43-72-3 6BFY43-73-3 6BFY43-74-3 6BFY43-75-3 6BFY43-76-3
6BFY44-72-2 6BFY44-73-2 6BFY44-74-2 6BFY44-75-2 6BFY44-76-2
6BFY42-72-3 6BFY42-73-3 6BFY42-74-3 6BFY42-75-3 6BFY42-76-3
6BFY43-72-2 6BFY43-73-2 6BFY43-74-2 6BFY43-75-2 6BFY43-76-2
Setting
Increase main jet calibration no.
(Gradually)
Decrease main jet calibration no.
(Gradually)
*In case of racing slight enrichment
of mixture reduces engine trouble.
7-6
Under 10°C
(86°F) (50°F)
(Winter)
#420 #460
6BFY43-74-
2 4
#37.5 #45
#42.5 #47.5
2-1/4 2-1/4
Diameter of straight portion
ø2.74 mm
(0.1079 in)
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
Discoloration of spark plug → If tan
color, it is in good condition.
If not effect:
Clogged air filter
Fuel overflow from carburetor
Clogged main air passage or
clogged filter
ENGINE
Sandy condition
15–25°C Over 30°C
(59–77°F) (86°F)
(Spring, Au- (Summer)
tumn)
#450 #440
6BFY44-74- 6BFY43-74-
3 3
#42.5 #40
#45 #42.5
2-1/4 2-1/4
ø2.75 mm ø2.76 mm
(0.1083 in) (0.1087 in)
Checking