9-1-2
PILOT
SYSTEM
The
pilot system supplies fuel
to
the
engine during idle and low
speed
operation.
The
fuel taken
through
the
main
jet
is
measured by
the
pilot jet
to
mix with
the
air
measured by the pilot air
jet
and
is
then regulated by
the
pilot screw
before
being supplied
to
the
engine through
the
pilot
outlet
and
by-pass.
During
idle
operation, the engine
is
supplied with fuel mainly through the pilot outlet.
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9-1-3
MAIN
SYSTEM
During medium and high-speed operation, fuel supply
to
the engine
is
controlled in the main
system, in which fuel flow
rate
is
controlled by the main
jet.
In
the main system, fuel
is
supplied through the main
jet
where
the
flow
rate
is
controlled, and through the main nozzle,
where
the
fuel
is
mixed with air, the flow
rate
of
which is controlled
by
the main
air
jet.
In
the
main nozzle the
metered
air
is
admitted through the bleed holes
to
mix with the fuel. The
mixture
is
then discharged through the top of the main nozzle
as
atomized fuel where it mixes
with intake
air
to
become
the
optimum air-fuel mixture
to
be
supplied
to
the
engine.
9-1-4
CHOKE
SYSTEM
The
choke
system aides starting in
the
cold
season by enriching
the
air-fuel mixture. When
the
engine is cranked with
the
choke
closed,
the
vacuum applied
to
the
main nozzle is made higher
so
that
more fuel
is
introduced into
the
air flow
to
make
a
starting easy.
9-2
DISASSEMBLY
and
REASSEMBLY
Besides mechanical failures, most troubles
are
attributed
to
an incorrect mixing ratio.
The
most common
causes
of
incorrect fuel-air mixtures
are
clogged
jets,
restricted
air
and fuel
passages, and variations in
the
fuel level.
In
order to obtain
the
full
performance
of
the
carburetor,
the
air cleaner and carburetor must
be
maintained clean
so
that
air and fuel
flow
n\
without restriction.
(See
Fig.
9-2-A,
9-2-B
or
9-2-C.)
9-2-1
THROTTLE
SYSTEM
1)
Unscrew Philips
head
screw
(16)
and remove
throttle
valve
(17)
and throttle shaft
(18).
2)
Remove throttle stop screw (20) to remove spring
(19).
Take
care
not
to
damage ends
of
throttle valve.
9-2-2
CHOKE
SYSTEM
1)
Unscrew Philips screw
(lo),
remove
choke
valve
(11)
and
take
out
choke
shaft
(12).
The
model
EY25-2,
EY27-2 engines have
choke
ball
(24)
and
choke
spring
(25)
in
the
carburetor.
Remove them beforehand
to
prevent them from being
lost.
2)
When assembling
choke
shaft,
the
flat on
choke
valve must
be
toward
the
main
air
jet
side-
9-2-3
PILOT
SYSTEM
1)
Remove pilot jet
(23).
Use
correct
tool to prevent damage.
2)
Unscrew pilot screw
(22)
and
remove spring
(21).
3)
Reassembly
a.
Tighten
pilot
jet firmly
to
prevent
fuel
leakage
and
a
possible
poor
engine performance.
b.
Replace pilot screw
if
tapered end is diformed.
Do
not overtighten.
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34
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