The working principie ofthe SAS for Quasar 250 cc Euro 2
engines is entirely similar to the SAS employed on 2-stroke
engines. The main differences are the following:
Secondary air enters directly into the exhaust duct on the
cylinder head, instead of entering through the exhaust pipe
as in two-stroke engines.
The reed valve found on 2-stroke engines is here replaced
by a membrane.
Unit «A", shown in the figure, is provided with a cut-off con-
nected to the vacuum inlet on the intake manifold to shut air
inlet during deceleration, so to prevent detonations in the
silencer. Air is sucked in through hole «B" and flows inside
the duct into air-box «C" where it is filtered by filtering ele-
The filtered air now enters membrane device «A", through
duct «E" and is then guided towards the head.
Flowing through pipe «F", flanged to the head, secondary
air reaches the exhaust duct thus providing oxygen addition
to the unburnt gases just before they enter the catalytic con
The efficiency of the catalyzing process is therefore increa-