Page 20
OPEN
Operation
at
High
Altitude
The
density
of
air
at
high
altitude
is
lower
than
at
sea level
.
Engine
power
is
reduced
as
the
air
mass
and
air-fuel ratio
decrease
.
Engine
power
and
generator
output will
be
reduced
approximately 3% for every 1000 feet
of
elevation
above
sea
level
.
This
is
a
natural
trend and
cannot
be
changed
by
adjusting
the
engine
.
At
high altitudes
increased
exhaust
emissions
can
also
result due
to
the
increased
enrichment
of
the
air
fuel
ratio
.
Other
high
altitude
issues
can
include
hard
starting
,
increased
fuel
consumption
and
spark
plug
fouling
.
To
alleviate
high
altitude
issues
other
than
the
natural
power
loss
,
FIRMAN
can
provide
a high
altitude
carburetor
main
jet
.
The
alternative
main jet
and
installation
instructions
can
be
obtained
by contacting
Customer
Support
.
Installation
instructions are
also
available
in
the
Technical
Bulletin
area
of
the FIRMAN
internet
site
.
The
part
number
and
recommended
minimum
altitude for
the
application
of
the
high
altitude
carburetor
main jet
is
listed
in
the
table
below
.
In
order
to
select
the
correct
high
altitude
main
jet it
is
necessary
to
identify
the
carburetor
model
.
For this
purpose
,
a
code
is
stamped
on
the
side
of
the
carburetor
.
Select
the
correct
main
jet
part
number corresponding
to
the
carburetor
code
found
on
your particular
carburetor
.
Operation
using
the
alternative
main
jet
at elevations
lower
than
the
recommended
minimum altitude
can
damage
the
engine
.
For
operation
at lower
elevations
,
the
standard
main
jet
must
be used
.
Operating
the
engine
with
the
wrong
engine
configuration
at
a
given
altitude
may
increase its
emissions
and
decrease
fuel
efficiency
and performance
.
WARNING
Standard main jet
Altitude main jet 1
Altitude main jet 2
439cc
490.131017.11
490.131017.12
490.131017.13
Altitude
3000-6000Feet
6000-8000Feet
0-3000Feet
