Air Induction System; Air Injection; Air Cut-Off Valve - Yamaha YBR125ED 2005 Service Manual

CARB

AIR INDUCTION SYSTEM

EAS00507
AIR INDUCTION SYSTEM

AIR INJECTION

The air induction system burns unburned
exhaust gases by injecting fresh air (second-
ary air) into the exhaust port, reducing the
emission of hydrocarbons.
When there is negative pressure 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
(1,112 to 1,292 °F).
EAS00508

AIR CUT-OFF VALVE

É The air cut-off valve is operated by the intake
gas pressure through the piston valve dia-
phragm. Normally, the air cut-off valve is open
to allow fresh air to flow into the exhaust port.
During sudden deceleration (the throttle valve
suddenly closes), negative pressure is gener-
ated and the air cut-off valve is closed in order
to prevent after-burning.
È
Additionally, at high engine speeds and when
the pressure decreases, the air cut-off valve
automatically closes to guard against a loss of
performance due to self-EGR.
È From the air filter case
É To the cylinder head
Ê To the intake manifold
Ê
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