..
Troubleshooting
Carburetor related
malfunctions
can
be
identif
ied
as
too rich or too lean a fuel m
ixtur
e.
Symptoms
are
as
follows
:
When
the fuel / air
mixture
is
too rich:
1. Engine noise is
dull
and
intermittent.
2. The
condition
grows
worse
when
the engine is
hot.
3 .
The
condition
grows
worse
when
the
enrichener
is opened.
4 . The
condition
may improve
slightly
when
the
air
silencer
is removed.
5. Exha ust gases are heavy.
6.
Spark plugs become fouled.
When
fuel/ air
mixture
is
too lean,
1. The engine becomes overheated.
2. The
condition
improves
when
the
enr
ic
hener
is
opened.
3. Acceleration is poor.
4 . Spark
pi
ugs burn.
5 . The revolutions
of
the
engine
fluctuate
and
lack of
power
is noticed.
If
a carburetor is experiencing too rich
or
too lean
fuel
mixture
problems,
first
check to see
that
the
throttle
is
work
ing properly. Then disassemble and
clean
the carburetor. A rich or lean
fuel
mixture
is
usually
caused by a clogged air or
fuel
passage. If
cleaning
does not improve
carburetor
performance,
carburetor
tuning
may be necessary.
MAXIMUM
Tuning
Different
fuel
metering
components
function
ac-
co
rding to the
throttle
setting
:
1.
Pilot
Air
Screw
-
from
closed
throttle
to one
half
throttle
opening.
2.
Throttle
Valve
Cutaway
-
from
closed
throttle
to
one ha
lf
throttle
ope
ning
.
3.
Jet
Ne
ed
le and -'Needle
Jet
- one e
ighth
to
seven
eighths
throttle
opening.
4.
Main
Jet
- one
quarter
to
full
throttle
opening.
5.
Econo
Jet
- one
half
to
full
throttle
opening.
Tuning
enables
adjustment
of
the fuel/
air
mixture
at any
throttle
setting by replacing the standard
fuel
metering
devices
with
parts designed to
meter
more or less fuel
than
standard
. Because a change
in
one fuel
metering
system
can
affect
the
per-
fo
rman
ce of other systems, all systems should be
checked
whenever
a
change
is made to one fuel
metering
system.
PILOT AIR SCREW - regulates air
that
mixes
with
fuel from the pilot jet.
Turning
the
pilot
air
screw
in
richens the fuel/
air
mixture
.
Turning
out
leans
the mixture. The
pilot
air
screw
should
be
normally
positioned 1/ 2 to 2
turns
from
full
in. Less
than
112
turn
indicates the
pilot
jet
is too small.
More
than
two
turns
out
indicates
the
pilot
jet
is too
large.
JET NEEDLE SYSTEM - can be
tuned
by changing
the
position
of
the
clip on
the
jet
needle. There are
five grooves at the top
of
the
needle. The grooves
are
numbered
1
through
5
from
top to bottom. The
clip is
normally
installed in
the
No.3
groove.
Mov
-
ing
the
clip
to
a
higher
position
on the needle
leans
out
the
fuel
/
air
mixture
.
Moving
the cl ip to a
lower
position richens
the
fuel
/
air
mixture
.
PILOT SYSTEM THROTTLE SLIDE I
EFFECT
MINIMUM
0
1/ 8
1/ 4
JET NEEDLE/ NEEDLE JET
3/ 8
1/ 2
3/ 4
THROTTLE POSITION
ECONO
JET
FULL
CARBURETOR
3-39
To Next Page
Loading...
