Road Condition And Examples Of Carburetor Setting; Examples Of Carburetor Setting Depending On Symptom - Yamaha YZ250 2021 Owner's Manual

EAM30601

ROAD CONDITION AND EXAMPLES OF CARBURETOR SETTING

Under 10 C
(50 F)
(Winter)
Main jet #178
N3CW-3
Jet needle
N3EW-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
General condition
15–25 C
Over 25 C
(59–77 F)
(77 F)
(Spring,
(Summer)
Autumn)
#178 #178
N3EW-2 N3EJ-2
N3CW-3 N3EW-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.
8-6
Sandy condition
15–25 C
Under 10 C
(59–77 F)
(50 F)
(Spring,
(Winter)
Autumn)
#182 #180
N3CW-3 N3CW-3
N3CW-4 N3EW-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
ENGINE
Over 25 C
(77 F)
(Summer)
#178
N3CW-3
N3EW-3
#52
+1/4
#50