KTM 400-660 LC4 1998-2005, Repair Manual

Page: 26 / 501

2-11E
5
3
2
1
4
Mode of operation of the secondary air system SAS (starting with the 2004 model)
Hot exhaust gases flow through the exhaust port
1
. The flow conditions in the exhaust port and the entire exhaust system's
influence on the escaping gas lead to a brief pressure drop in the exhaust port (vacuum).
The secondary air valve (SAS)
2
opens during these cyclic vacuum stages, supplying oxygen to the hot exhaust gas through the
line
3
.
The secondary air valve prevents exhaust gas blowback into the environment.
In an overrun condition (extreme vacuum in the intake port)the SAS valve 2 will interrupt the air supply to the exhaust port to
prevent any exhaust backfire.
The control valve is regulated by a control line
4
. The control line transfers the vacuum from the intake port
5
to the control
valve.
The control valve is open in the lower part-load operation (slight vacuum in the intake port).
The reaction between the atmospheric oxygen and the toxic constituents of the exhaust gas (CO - carbon monoxide and
HC - hydrocarbon) leads to a significant reduction of pollutants through the afterburning of CO and HC and a dilution of the
exhaust gas.
NOTE: The secondary air system does not influence the engine performance.