Yamaha YZ250 2022, Owner'S Service Manual

Page: 262 / 274

ENGINE
10-7
EAM30601
ROAD CONDITION AND EXAMPLES OF CARBURETOR SETTING
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.
EAM30602
EXAMPLES OF CARBURETOR SETTING DEPENDING ON SYMPTOM
General condition Sandy condition
Under 10

C
(50

F)
(Winter)
15–25

C
(59–77

F)
(Spring,
Autumn)
Over 25

C
(77

F)
(Summer)
Under 10

C
(50

F)
(Winter)
15–25

C
(59–77

F)
(Spring,
Autumn)
Over 25

C
(77

F)
(Summer)
Main jet #178 #178 #178 #182 #180 #178
Jet needle N3CW-3 N3EW-2 N3EJ-2 N3CW-3 N3CW-3 N3CW-3
Pilot jet #50 #50 #50 #52 #52 #52
Pilot air screw -1/4 0 0 0 0 +1/4
Power jet #50 #50 #50 #50 #50 #50
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
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 Lower jet needle clip position. (1
groove down)
1. Groove 1
2. Groove 2
3. Groove 3
4. Groove 4
5. Groove 5
6. Jet needle
7. Clip
Leaner
(Standard)
Richer
Rich mixture Raise jet needle clip position. (1
groove up)
•
1/4–3/4 throttle
*Hard breathing
Lack of speed
Lower jet needle clip position. (1
groove down)
•
1/4–1/2 throttle
Slow speed pick-up
White smoke
Poor acceleration
Raise jet needle clip position. (1
groove up)
The clip position is the jet needle
groove on which the clip is installed.
The positions are numbered from the
top.