Yamaha 2002 TDM900, Service Manual

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1-19
FEATURES
GEN
INFO
1 Air cut-off valve
2 Reed valve
3 Exhaust port
4 Air filter case
AIR INDUCTION SYSTEM
The air induction system (AI system) introduces fresh air into the exhaust port in order to burn the un-
burned gas (which is present in the exhaust gas) in the exhaust pipe. The burning of the unburned
gases in this manner enhances the efficiency of the catalyst and results in cleaner exhaust gases.
The AI system takes a portion of the air from the air cleaner, sends it to the reed valve via the air cut-off
valve, and introduces it directly into the exhaust port through the reed valve.
The air cut-off valve is controlled by the signals from the ECU in accordance with the combustion condi-
tions. Ordinarily, the air cut-off valve opens to allow the air to flow during idle and closes to cut off the
flow when the motorcycle is being driven. However, if the coolant temperature is below the specified
value, the air cut-off valve remains open and allows the air to flow into the exhaust pipe until the temper-
ature becomes higher than the specified value.
The reed valve is provided on the cylinder head cover above the cylinders, and sends air to the exhaust
pipe through the inside of the cylinder head.