Table of Contents
Advertisement
The carburetor on your CR should perform
suitably with the standard recommended settings
under average load, climatic, and barometric
conditions. However, to fine tune the engine's
power output, the carburetor may require
adjustments for specific competition needs.
Optional main jets and slow jets are available for
your CR. See your Honda dealer.
Any engine or airbox modifications or the use of
an aftermarket exhaust system may require
jetting changes.
Carburetor Components
Starting Circuit
A very rich mixture must be delivered to the
cylinder when the engine is being started. When
the choke knob (1) is pulled up, fuel is metered
by the starter jet (2) and is mixed with air from
the air passage (3) to provide a rich mixture for
starting. The mixture discharges through the
orifice (4) into the cylinder.
(4)
(3)
(2)
(1) choke knob
(3) air passage
(2) starter jet
(4) orifice
Slow Circuit
Fuel is metered by the slow jet (5) and is mixed
with air that has been metered by the air screw
(6). The mixture enters the venturi through the
bypass (7) and slow jet outlet (8).
(6)
(5) slow jet
(6) air screw
Main Circuit
Fuel is metered by the main jet (9), jet needle
(10) and needle jet (11). It is then mixed with air
(1)
coming from the air jet (12) and enters the
venturi past the needle jet.
Baffle Plate
The baffle plate (13) prevents foaming of fuel or
abnormal fuel level around the main jet.
Float Chamber
The float (14) and float valve (15) operate to
maintain a constant level of fuel in the float
chamber.
Carburetor Adjustments & Tuning Tips
(7)
(9) main jet
(10) jet needle
(11) needle jet
(12) air jet
(8)
Carburetor Circuit Functions
The carburetor has several major circuits, each
(5)
providing the fuel/air mixture over a given
portion of throttle valve opening.
(7) bypass
(8) slow jet outlet
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.
Your CR's carburetor jet sizes are numbered in
increments of 10. When changing the main jet
size, increase or decrease it gradually until the
desired jetting is obtained. Because your CR's jet
size numbers do not correspond with other
carburetor manufacturer's jet size numbers, use
genuine Honda CR250R jets.
(12)
(14)
(11)
(15)
(10)
(13)
(9)
(13) baffle plate
(14) float
(15) float valve
MAIN JET
JET NEEDLE (TAPERED SECTION)
JET NEEDLE
(STRAIGHT SECTION)
SLOW JET AND AIR SCREW
1/4
3/4
FULLY
FULLY
1/8
1/2
OPENED
CLOSE
Adjustments for Competition
(cont'd)
103
Hide quick links:
Advertisement
Table of Contents
