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Carburetor Adjustments & Tuning Tips
112
Adjustments for Competition
The carburetor has several major circuits, each
providing 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 (1/2) to
full throttle (4/4). The size should be reduced at
higher altitudes.
Honda carburetor jet sizes are numbered in
increments 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
manufacturer’s jet size numbers, use only Honda
jets.
Jet Needle
The jet needle controls fuel/air mixture over fully
closed to 3/4 throttle. The straight section (1)
affects throttle response at smaller throttle
openings. By changing the position of the clip (2)
in its groove, you can improve acceleration 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 performance.
• If the engine blubbers (rich) exiting a corner,
turn the pilot screw clockwise to lean the
mixture.
• If the engine surges (lean) exiting a corner,
turn the pilot screw counterclockwise to richen
the mixture.
The minimum to maximum range of pilot screw
adjustment is 1 1/2 to 2 1/4 turns out from the
lightly seated position. If you exceed 2 1/4 turns
out, the next larger slow jet is needed.
If you are under 1 1/2 turns out, the next smaller
slow jet is needed.
Leak jet
The smaller the number, the smaller the jet bore
diameter. This controls the amount of fuel returned
to the float chamber under pressure, therefore the
flow amount is increased or decreased. With a
small jet, pressure is raised faster and the elapsed
time before the fuel starts flowing is shorter.
1. Remove the seat and fuel tank (pages 29, 30).
2. Drain the remaining fuel in the float bowl by
loosening the drain screw (1).
3. Drain the carburetor into an approved gasoline
container and dispose of it in an approved
manner (page 130).
NOTICE
Improper disposal of drained fluids is harmful to
the environment.
Carburetor Circuit Functions
(1) straight section (2) clip
(2)
(1)
LEANER
RICHER
1st
2nd
3rd
4th
5th
Carburetor Removal
WARNING
Gasoline is highly flammable and
explosive. You can be burned or seriously
injured when handling fuel.
• Stop the engine and keep heat, sparks
and flame away.
• Handle fuel only outdoors.
• Wipe up spills immediately.
(1) drain screw
(1)
31KSE7100_NA.book 112 ページ ２０１９年４月９日 火曜日 午後１時１３分
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