Road Condition And Examples Of Carburetor Setting; Specifications Of Jet Needle; Examples Of Carburetor Setting Depending On Symptom - Yamaha YZ125X 2021 Owner's Service Manual

EAM30601

ROAD CONDITION AND EXAMPLES OF CARBURETOR SETTING

Under 10 C
(50 F)
(Winter)
Main jet #440
Jet needle 6BFY44-74-3 6BFY43-74-3 6BFY44-74-2 6BFY43-74-4 6BFY44-74-3 6BFY43-74-3
Pilot jet #42.5
Pilot air
2-1/4
screw
TIP
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 "1",
add "1" to the value chosen in the chart.
EAM30600

SPECIFICATIONS OF JET NEEDLE

ø2.72 mm
(0.1071 in)
Rich 1 richer 6BFY43-72-4
6BFY44-72-3
0.5 richer
6BFY42-72-4
STD 6BFY43-72-3
6BFY44-72-2
0.5 leaner
6BFY42-72-3
Lean 1 leaner 6BFY43-72-2
EAM30602

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
Speed pick-up stops
Slow speed pick-up
Slow response
Sooty spark plug

Rich mixture
General condition
15–25 C
Over 30 C
(59–77 F)
(86 F)
(Spring,
(Summer)
Autumn)
#430 #420
#40 #37.5
2-1/4 2-1/4
Diameter of straight portion
ø2.73 mm
(0.1075 in)
6BFY43-73-4
6BFY44-73-3
6BFY42-73-4
6BFY43-73-3
6BFY44-73-2
6BFY42-73-3
6BFY43-73-2
Setting
Increase main jet calibration no.
(Gradually)
Decrease main jet calibration no.
(Gradually)
*In case of racing slight enrichment of
mixture reduces engine trouble.
10-5
Sandy condition
15–25 C
Under 10 C
(59–77 F)
(50 F)
(Spring,
(Winter)
Autumn)
#460 #450
#45 #42.5
2-1/4 2-1/4
ø2.74 mm ø2.75 mm
(0.1079 in) (0.1083 in)
6BFY43-74-4 6BFY43-75-4
6BFY44-74-3 6BFY44-75-3
6BFY42-74-4 6BFY42-75-4
6BFY43-74-3 6BFY43-75-3
6BFY44-74-2 6BFY44-75-2
6BFY42-74-3 6BFY42-75-3
6BFY43-74-2 6BFY43-75-2
• 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 cannot be corrected:
Clogged air filter
Fuel overflow from carburetor
Clogged main air passage or
clogged filter
ENGINE
Over 30 C
(86 F)
(Summer)
#440
#40
2-1/4
ø2.76 mm
(0.1087 in)
6BFY43-76-4
6BFY44-76-3
6BFY42-76-4
6BFY43-76-3
6BFY44-76-2
6BFY42-76-3
6BFY43-76-2
Checking