Checking The Air Induction System - Yamaha XT250X 2008 Service Manual

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.
B
A. From the air filter
B. From the intake manifold
C. To the cylinder head
1. Check:
Hoses
G
Loose connections → Connect properly.
Cracks/damage → Replace.
Pipes
G
Cracks/damage → Replace.
Refer to "CYLINDER HEAD" on page 5-6.
2. Check:
Air cut-off valve
G
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A
C
6-12
AIR INDUCTION SYSTEM
Cracks/damage → Replace the reed valve.