Honda CRF450R Owner's Manual page 71

Circuit Adjustments
The carburetor has several major circuits, each provid-
ing the fuel/air mixture over a given portion of throttle
valve opening.
These major circuits overlap as shown below.
• Main Jet
The main jet affects fuel/air ratio from half to full throttle
(4/4). The size should be reduced at higher altitudes.
NOTE:
• Honda carburetor jet sizes are numbered in incre-
ments of 2 or 3. When changing the main jet size,
increase or decrease it gradually until the desired
jetting is obtained. Because Honda jet size numbers
do not correspond with other carburetor manu-
facturer's jet size numbers, use genuine 2004 Honda
CRF450R jets.
• Jet Needle
The jet needle controls fuel/air mixture over fully closed
to 3/4 throttle. The straight section affects throttle re-
sponse at smaIIer throttle openings. By changing the
position of the clip in its groove, you can improve ac-
celeration at medium low and medium speed.
• Slow Jet and Pilot Screw
The slow jet and pilot screw affects fuel/air ratio over
fully closed to 1/4 throttle.
Adjust the pilot screw to obtain the best off-idle perfor-
mance.
• If the engine blubbers (rich) exiting a corner, turn
the pilot screw clockwise to lean the mixture.
• If the engine surges (Iean) exiting a corner, turn the
pilot screw counter clockwise to richen the mixture.
NOTE:
• The minimum to maximum range of pilot screw ad-
justment is 1/2 to 2 1/2 turns out from the lightly
seated position.
If you exceed 2 1/2 turns out, the next larger slow
jet is needed.
If you are under 1/2 turns out, the next smaller slow
jet is needed.
Carburetor Major Adjustments
NOTE:
• For the following recommendations to be accurate,
you must use the standard jetting as a baseline. Also,
don't change any of the settings until you've deter-
mined what changes are necessary.
Standard settings:
Pilot screw opening – 1 1/2 turns out
Slow jet – #42
Jet needle – NCYR
Needle clip position – 4th groove
Main jet – #165
Float level – 0.31 in (8.0 mm)
identification number – FCR00C
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