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FUEL SYSTEM
HIGH ALTITUDE ADJUSTMENT
(except U type)
5-20
At high altitude, the
standard
carburetor
air-fuel
mixture will be too
rich.
Performance
will
decrease,
and fuel consumption will increase. A
very
rich
mix-
ture will also foul the
spark
plug and
cause
hard
starting. Operation at an
altitude
that differs from
that
at which
this engine
was
certi
fied, for
extended
periods
of
time, may
increase emissions.
High altitude performance
can
be
improved by spe-
cific
modifications to the
carburetor. If your cus-
tomer
always operates the
A TV at altitudes
above
6,500
feet
(2.000
meters).
you should perform this
carburetor
modification
.
Even with
carbu
retor
modification, engine
horse-
power
will
decrease
about
3.5% for each 1
,ODD-foot
(300-meter)
i
ncrease
in altitude.
The
effect
of alti-
tude
on
horsepower
will
be grea ter than this
if
no
carburetor
modification
is
made.
This
engine, when operated at
high altitude
with
the
carburetor
modifications for high altitude
use,
will
meet
each emission standard
throughout
its
useful
life.
The high altitude
carburetor
adjustment is per-
formed as
follows:
Remove the
carburetor (page
5-6)
and
the floa
t
chamber.
Replace the
standard
main jet
with
the high altitude
type.
HIGH ALTITUDE MAIN
JET:
11 158
Check that the O-ring
on
the float
chamber is in
good condition and
replace
it
with a new
one
if
necessary.
Install
the
floal chamber
and the
carburetor.
Screw
in
the pilot
screw
the
specified
number
of
turns from the factory preset position using the
spe-
cial
tool.
TOOL:
Pilot
screw
w
ren ch
07KMA·MN90101
or
07KMA·MN9Al00
(U
.S.A
.onlv)
HIGH
ALTITUDE
PILOT
SCREW
OPENING:
114
tum in from
initial
opening
Start
the
engine and
warm it
up.
Adjust the idle
speed
at high altitude
w
ith the throt-
tle stop screw to
ensure
proper high altitude
opera-
tion.
IDLE
SPEED:
1,400:t 100 rpm
(min"
,
NOTICE
when the
carburetor
has been modified
for
high
alti-
tude
operation,
the
air-fuel
mixture will be too
lean
for
low
altitude
use.
Operation at
altitudes
below
5,000
feet (1,500 m}
with
a modified carburetor may
cause the engine overheat, resulting in serious
engine damage and increased exhaust
emissions.
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