Honda Crf 250 M Manual

Adjustments for Competition117
Carburetor Adjustments & Tuning Tips
Carburetor Circuit Functions
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.
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...

Carburetor Adjustments & Tuning Tips
118Adjustments for Competition
4. Disconnect the fuel line (2) from the fuel
valve (3).
5. Remove the fuel tank (page 30).
6. Remove the sub-frame (page 32).
7. Loosen the intake band screw (4).
(2) fuel line
(3) fuel valve
(4) intake band screw
8. Disconnect the throttle sensor connector (5).
9. Remove the carburetor.
(5) throttle sensor connector
10.Remove the hot start cable holder (6).
(6)  hot start cable holder
11. Disconnect the rear suspension (7) upper...

Carburetor Adjustments & Tuning Tips
Adjustments for Competition119
Carburetor Disassembly
1. Pull up the cable clamp (1) and remove the
carburetor top bolts (2).
Then remove the carburetor top (3).
(1) cable clamp
(2) carburetor top bolts
(3) carburetor top
2. Remove the jet needle holder (4) and jet
needle (5) from the throttle valve (6).
(4) jet needle holder
(5) jet needle
(6) throttle valve
3. Remove the link arm set screw (7).
When installing the link arm set screw, apply
a locking agent to the...

Carburetor Adjustments & Tuning Tips
120Adjustments for Competition
5. Remove the accelerator pump cover screws
(12) and accelerator pump cover (13).
(12) accelerator pump cover screws
(13) accelerator pump cover
6. Remove the D-ring (14), O-ring (15) spring
(16) and diaphragm (17).
Clean the diaphragm.
When installing the D-ring into the accelerator
pump cover (13) make sure the D-rings
flatside faces down, away from the float bowl
(18).
(13) accelerator pump cover (16) spring
(14) D-ring (17)...

Carburetor Adjustments & Tuning Tips
Adjustments for Competition121
Carburetor Assembly
To assemble, reverse the disassembly procedures.
To install the carburetor, reverse the removal
procedures.
•  After installing the carburetor, adjust the
throttle cable (1) free play and hot start cable
(2) free play.
•  After installing the carburetor, check the air
vent hoses (3) and overflow hose (4) for
kinking or pinching and correct routing as
necessary.
(1) throttle cables
(2) hot start cable(3) air vent...

Carburetor Adjustments & Tuning Tips
122Adjustments for Competition
Standard Tuning Recommendations
For the following recommendations to be
accurate, you must use the standard settings as a
baseline.  Also, don’t change any of the settings
until you’ve determined what changes are
necessary.
Adjustment
Pilot screw opening
Slow jet
Jet needle
Needle clip position
Main jet
Float level
Identification number
Standard settings
1–3/4 turns out
#42
NCYQ
3rd groove
#172
0.31 in (8.0 mm)
FCR01B
Adjustments for...

Carburetor Adjustments & Tuning Tips
Adjustments for Competition123
Special Tuning Conditions
There are some unique atmospheric conditions or
situations that may require additional
adjustments.
It should not be necessary to go more than one
jet size richer or leaner to fine tune your
motorcycle.  If larger jetting changes are
necessary, check for air leaks, blocked or
restricted exhaust or fuel systems, or a dirty air
cleaner.
Condition
long straights
uphill sections
sand
mud
high humidity
raining
hotter...

Carburetor Adjustments & Tuning Tips
124Adjustments for Competition
Carburetor Minor Adjustments
The standard carburetor  settings are ideal for the
following conditions: sea level altitude, and 20°C
(68 °F) air temperature.  If your conditions are
different, you may need to adjust the carburetor
settings, using the tuning information on page
122 and 123. Confirm your settings are correct
before proceeding.
Minor 
Adjustments
1. Adjust the carburetor setting using the tuning
information on page 122 and...

Carburetor Adjustments & Tuning Tips
Adjustments for Competition125 11. Change the main jet (3) and slow jet (4) as
required.
(3) main jet
(4) slow jet
12. Reinstall the float bowl plug.
13.If you’ve determined that the jet needle or clip
position of jet needle must be changed, you
must remove the carburetor top.14.Remove the fuel tank (page 30).
15. Rotate the carburetor to the left and remove the
carburetor top bolts (5) and carburetor top (6).
(5) carburetor top bolts
(6) carburetor top
16.Remove the...

Carburetor Adjustments & Tuning Tips
126Adjustments for Competition
Spark Plug Reading
Refer to Spark Plugon page 54.
Check any jetting change by reading the spark
plug.  The following procedure is recommended.
You may not get an accurate reading if you
simply turn off the engine and pull the plug for
inspection.
Use a new spark plug.  Inspect the plug before
installing it.Using spark plugs with an improper heat range
or incorrect reach can cause engine damage.
Before removing the spark plug, clean the...