Road Condition And Examples Of Carburetor Setting - Yamaha YZ250 2022 Owner's Service Manual

EAM30601

ROAD CONDITION AND EXAMPLES OF CARBURETOR SETTING

Under 10 C
(50 F)
(Winter)
Main jet #178
Jet needle N3CW-3
Pilot jet #50
Pilot air screw -1/4
Power jet #50
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
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
Lean mixture
Rich mixture
• 1/4–3/4 throttle
*Hard breathing
Lack of speed
• 1/4–1/2 throttle
Slow speed pick-up
White smoke
Poor acceleration
General condition
15–25 C
Over 25 C
(59–77 F)
(77 F)
(Spring,
(Summer)
Autumn)
#178 #178
N3EW-2 N3EJ-2
#50 #50
0 0
#50 #50
Setting
Increase main jet calibration no.
(Gradually)
Decrease main jet calibration no.
(Gradually)
*In case of racing slight enrichment of
mixture reduces engine trouble.
Lower jet needle clip position. (1
groove down)
Raise jet needle clip position. (1
groove up)
Lower jet needle clip position. (1
groove down)
Raise jet needle clip position. (1
groove up)
10-7
Sandy condition
15–25 C
Under 10 C
(59–77 F)
(50 F)
(Spring,
(Winter)
Autumn)
#182 #180
N3CW-3 N3CW-3
#52 #52
0 0
#50 #50
Checking
• 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
1. Groove 1
2. Groove 2
3. Groove 3
4. Groove 4
5. Groove 5
6. Jet needle
7. Clip
The clip position is the jet needle
groove on which the clip is installed.
The positions are numbered from the
top.
ENGINE
Over 25 C
(77 F)
(Summer)
#178
N3CW-3
#52
+1/4
#50
Leaner
(Standard)
Richer