Yamaha YZ450F, Owner'S Service Manual

Page: 604 / 650

7 - 2
T U N
CAUTION:
• The carburetor is extremely sensitive to
foreign matter (dirt, sand, water, etc.).
During installation, do not allow foreign
matter to get into the carburetor.
• Always handle the carburetor and its
components carefully. Even slight
scratches, bends or damage to carburetor
parts may prevent the carburetor from
functioning correctly. Carefully perform
all servicing with the appropriate tools
and without applying excessive force.
• When the engine is stopped or when
riding at no load, do not open and close
the throttle unnecessarily. Otherwise, too
much fuel may be discharged, starting
may become difficult or the engine may
not run well.
• After installing the carburetor, check that
the throttle operates correctly and opens
and closes smoothly.
Atmospheric conditions and carburetor
settings
The air density (i.e., concentration of oxygen
in the air) determines the richness or lean-
ness of the air/fuel mixture. Therefore, refer
to the above table for mixture settings.
That is:
• Higher temperature expands the air with its
resultant reduced density.
• Higher humidity reduces the amount of oxy-
gen in the air by so much of the water vapor
in the same air.
• Lower atmospheric pressure (at a high alti-
tude) reduces the density of the air.
Air temp. Humidity
Air
pressure
(altitude) Mixture Setting
High High Low (high) Richer Leaner
Low Low High (low) Leaner Richer
SETTING