Yamaha XT250X 2008, Service Manual, Page: 223 / 282

AIR INDUCTION SYSTEM
6-12
EAS27060
CHECKING THE AIR INDUCTION SYSTEM
Air induction
The air induction system burns unburned ex-
haust gases by injecting fresh air (secondary air)
into the exhaust port, reducing the emission of
carbon monoxide. When there is negative pres-
sure at the exhaust port, the reed valve opens,
allowing secondary air to flow into the exhaust
port. The required temperature for burning the
unburned exhaust gases is approximately 600
to 700
°
C.
Air cut-off valve
The air cut-off valve is controlled by the intake
gas pressure from the intake manifold. Ordinari-
ly, the air cut-off valve opens to allow the air to
flow during idle and closes to cut-off the flow
when the vehicle is being driven. If the pressure
drops when the engine speed is high, the
air-cutoff valve is closed automatically.
1. Check:
●
Hoses
Loose connections
→
Connect properly.
Cracks/damage
→
Replace.
●
Pipes
Cracks/damage
→
Replace.
Refer to “CYLINDER HEAD” on page 5-6.
2. Check:
●
Air cut-off valve
Cracks/damage
→
Replace the reed valve.
A. From the air filter
B. From the intake manifold
C. To the cylinder head
A
B
C
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