Checking The Air Induction System - Yamaha WR250R 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
hydrocarbons. When there is negative pressure
at the exhaust port, the reed valve opens, allow-
ing secondary air to flow into the exhaust port.
The required temperature for burning the un-
burned exhaust gases is approximately 600 to
700°C.
Air cut-off valve
The air cut-off valve is controlled by the signals
from the ECU in accordance with the combus-
tion conditions. Ordinarily, 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 be-
ing driven.
A. From the air filter
B. To the cylinder head
1. Check:
Hoses
G
Loose connections → Connect properly.
Cracks/damage → Replace.
Pipes
G
Cracks/damage → Replace.
2. Check:
Reed valve
G
Reed valve stopper
G
Reed valve seat
G
Cracks/damage → Replace the reed valve.
A
B
7-12
AIR INDUCTION SYSTEM
3. Check:
Air cut-off valve
G
Cracks/damage → Replace.