Functional Characteristics Of The Secondary Air System (Sls) - KTM 400-660 LC4 1998-2005 Repair Manual

2-10E

Functional characteristics of the secondary air system (SLS)

1
When the exhaust valve is open, the hot exhaust gases flow through the exhaust port at a very high speed. As a consequence
of the flow conditions in the exhaust port and due to the influence exerted by the entire exhaust system on the escaping gases,
the pressure in the exhaust port drops temporarily (underpressure).
During these cyclic underpressure phases, the secondary air valve 2 opens, thus adding oxygen of the air to the hot exhaust
3
gases through pipe .
At higher engine speeds, the secondary air valve interrupts the oxygen supply to prevent overheating of the catalytic converter.
4
Additionally, the secondary air valve prevents the exhaust gases from flowing back into the air filter box .
5
When the motorcycle is pushed (high underpressure in the intake port) the control valve (ASV) interrupts the air flow into the
exhaust port to prevent exhaust detonations.
6 7
The control valve is controlled via a control pipe . This control pipe transmits the underpressure from the intake port to the
control valve.
During normal operation (slight underpressure in the intake port), the control valve is open.
The reaction between the oxygen of the air and the harmful components of the exhaust gases (CO - carbon monoxide, HC -
hydrocarbon) reduces the content of harmful substances by approximately 50%. The use of a catalytic converter, in combination
with the SLS, allows an additional significant reduction of pollutant emissions.
6
3
5
4
2
1
7