4)
MID-RANGE
OPERATION
If
only
reduced engine output is required and the
throttle valve
is
accordingly portially closed,
a
vacuum
sufficient to
suck
fuel
is
present only
in
the
space between the throttle valve and the en-
gine. The fuel now
only
flows
through the idling
system.
As
a result,
the
non-return valve
(V)
in the
N
main system closes, thus preventing air
from
en-
tering the pressure regulator, where it could im-
pede the fuel flow.
5)
IDLING
OPERATION
When the engine
is
idling, the throttle valve is
so
far
closed that the vacuum between the valve and
the engine
only
acts
on
the idling outlet drilling
(LA).
While fuel is being sucked out
of
the idling
outlet drilling
(LA),
air
is
entering the bypass
drilling
(BP),
which mixes with the fuel coming
out.
The
idling speed
is
set with the stop screw
GAS)
and
the matching fuel quantity with idle mixture
screw
(L).
6)
STARTING
To
start the engine, the choke
is
closed, with the
throttle valve
@>
roughly
half-open.
Each attempt to
start
the engine produces a vac-
uum
in the carburetor
port,
which draws fuel
through
both jet systems.
When starting
a
hot or cold engine, the carburetor
must first
be
filled with fuel,
as
air
and fuel vapour
must be flushed out of the carburetor systems.
Several attempts at starting-usually
four,
are
nec-
essary before the first firing occurs.
The choke must then be opened and the next
attempt will
start
the engine
running.
n
Fig.
9-7
-
42
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