Pre-Adjustment Checks
- Air cleaner
- Air leaks
- Float level
- Clogged jets
- Spark plug fouling (improper heat range or other cause)
- Fuel freshness
- Owner modifications (such as exhaust pipe, holes in air
box, etc.)
Standard Tuning
Recommendations
As delivered, with an exhaust diffuser installed in the exhaust pipe and a noise
suppressor installed in the air box, your bike may be jetted rich for your
riding needs. The standard settings offer maximum performance for closed course
competition -- after removal of the exhaust diffuser and noise suppressor. The
standard settings also prevent the possibility of engine damage if an you remove
the diffuser and suppressor for closed course competition without making a
jetting change. For maximum trail riding performance (diffuser and suppressor
installed), adjust as shown below.
| |
Standard
Settings (as delivered) |
Settings
for Trail Riding* |
| Pilot
Screw |
2¼ turns out |
2¼ turns out ± ¾ turns |
| Slow
Jet |
#62 |
#60 |
| Needle
Clip |
3rd groove (from
top) |
2nd groove (from
top) |
| Main
Jet |
#162 |
#158 |
| Float
Level |
14.5mm
(0.57") |
| Carb
ID |
PDKLA |
*noise suppressor and exhaust diffuser installed
Adjustments for Altitude & Temperature
All jetting recommendations are based on standard jetting
with an un-modified engine. The following conditions can
affect the fuel mixture.
| Condition |
Mixture will be |
Adjustment |
| Cold Temp |
Lean |
Richer |
| Warm Temp |
Rich |
Leaner |
| Dry Air |
Lean |
Richer |
| High Humidity |
Rich |
Leaner |
| High Altitude |
Rich |
Leaner |
Correction Factor Charts
Use the applicable correction factor charts shown below
to determine if carburetor adjustments are needed because
of changes in temperature and/or altitude.
| Main Jet Correction Factors |
Main Jet Correction Factors |
| Standard Settings (as delivered)* |
Trail Riding Settings |
| (noise suppressor & exhaust diffuser installed) |
(noise suppressor & exhaust diffuser installed) |
 |
 |
| *If the correction factor is 0.95 or less, turn pilot screw in ¼ turn. |
- Plot a straight line up from the temp to the horizontal
line of altitude.
- At the intersection of these two lines, plot a horizontal
line to the left edge of the chart.
- Multiply the correction factor times your jet size. Round
the resulting number up or down to the nearest jet size.
(Honda main jet and slow jet sizes are numbered in increments
of 2 or 3.)
- With Trail Riding Settings (noise suppressor and exhaust
diffuser installed), you will find your bike is more sensitive
to altitude and temperature changes. For this reason, correction
factor charts are given for both the main and slow jets.
Also note the range of possible fine tuning of the pilot
screw (± ¾ turn).
| Slow Jet Correction Factors |
| Trail Riding Settings |
| (noise suppressor & exhaust diffuser installed) |
 |
Example: At a temp of 35ºC (95ºF) and an altitude of 1,000
m (3,280 ft), recommended carburetion is:
Standard Settings, as delivered:
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 bike. If larger jetting changes are necessary, check
for air leaks, blocked or restricted exhaust or fuel systems, or a dirty air
filter.
| Condition |
Main
Jet Adjustment |
| Long Straights |
Next Larger |
| Uphill Sections |
| Sand |
| Mud |
| High Humidity |
Next Smaller |
| Raining |
| Hotter than 113ºF (59ºC) |
Adjustment
Procedures
To
prevent engine damage, always adjust the main jet before adjusting the jet
needle. If there is any doubt, always choose the next richer jet (larger) so there is a
margin for safety. You can make the following internal adjustments without
removing the carburetor from the engine:
- Main Jet
- Slow Jet
- Needle Clip Position
You may find it easier to remove the carburetor to change the
needle clip position. Removal is time consuming, but makes the
actual adjustment easier. To change the main jet, the float bowl
must be drained. To change the slow jet, the float bowl must
be drained and removed. To avoid spilling fuel on a hot engine,
remove the float bowl only when the engine is cool.
- Warm up the engine for 10-15 minutes.
- Ride a practice lap with the standard jetting and a new spark
plug. Note engine acceleration and response in relation to
the throttle opening.
- Verify carburetion by removing the spark plug and reading
its firing end.
- Consider engine response, altitude and temperature conditions
(from tables above). Then decide what carburetor settings or
replacement jets may be necessary.
- Turn the fuel valve OFF.
- Place an approved gasoline container under the drain tube.
- Using a flat screwdriver, turn the drain screw counterclockwise
to drain the float bowl.
Pilot Screw
Simple, use
the pilot screw to adjust the idle mixture. Turn the pilot screw in to lean out
the idle mixture or turn the pilot screw out to richen or fatten up the idle
mixture.
Slow Jet
| |
 |
| 1 - Choke Lever |
| 2 - Float Bowl |
| 3 - Baffle Plate |
| 4 - Main Jet |
| 5 - Baffle Plate Notch |
| 6 - Slow Jet |
Honda carburetor jet sizes are
numbered in increments of 2 or 3. When changing the slow jet size, increase or
decrease it gradually until the desired jetting is obtained. Use only genuine
Honda jets because Honda jet size numbers do not
correspond with other carburetor manufacturer's jet size numbers. It is not
necessary to remove the carburetor to change the slow jet.
- Push the choke lever (1) up out of the way (ON position).
- Using a short Phillips screwdriver, remove the three screws
securing the float bowl (2).
- Carefully lower the float bowl. Check that the baffle plate
(3) surrounding the main jet (4) is not disturbed during removal
of the float bowl.
- Note the location of the baffle plate notch (5) in relation
to the overflow pipe. The baffle plate must be reinstalled in
this position.
- Remove the baffle plate.
- Using a flat screwdriver, carefully remove the slow jet (6).
- Install the new slow jet.
- Making sure the notch in the baffle plate is located to fit
around the overflow pipe, install the baffle plate.
- Install the carburetor float bowl.
- Lower the choke lever to its OFF position.
Needle Clip Position
- It is not necessary to remove the carburetor to change the
needle clip position.
- Remove the seat.
- Remove the fuel tank.
- Remove the sub-frame.
- Loosen the front insulator mounting clamp. From the right
side, leaving the cables attached, slide the carb out of the
insulator.
- Using a Phillips screwdriver, remove the two screws and the
carburetor top.
Using
a Phillips screwdriver and taking care that the lock washer
doesn't fall into the carburetor, remove the screw and lock
washer on the slide actuating arm.
- Using a Phillips screwdriver, remove the two screws that
connect the slide actuating arm to the slide.
- Leaving the screws in place in the connector piece, lift
the actuating arm and connector piece out of the carburetor
body. Pull it up and flip it rearward out of the way.
- Lift the slide out of the carburetor body.
- Slide the needle up and remove it from the slide.
- Change the clip position (raise clip to lower needle, lower
clip to raise needle).
- Reinstall the parts in the reverse order of removal.
Main Jet
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. Use only genuine
Honda jets because Honda jet size numbers do not
correspond with other carburetor manufacturer's jet size numbers. It is not
necessary to remove the carburetor to change the main jet.
- Remove the float bowl plug (17mm wrench).
- Using a socket wrench or main jet tool (6mm), remove
the main jet.
- Insert and tighten the new main jet.
- Check the 0-ring of the float bowl plug and reinstall
it.
Float Adjustment
Sometimes it may be necessary to remove the carburetor and
the throttle cables to adjust the float height.
Hold
the carburetor in a position where the float arm tang will
just close the float valve without compressing the spring-loaded
pin in the end of the float valve needle. To avoid possible
damage, do not press the float against the float valve.
- Float Height: 14.5 mm (0.57 in)
- Position the float height gauge against the carburetor
body. If the gauge has been set to the specified float
height, it should just touch the float without causing
the float to move.
- If the float height is not correct, carefully bend the
float arm tang toward or away from the float valve until
the specified float height is obtained. Replace a float
that is damaged or extremely misaligned. Remember that
vent tube routing is critical. Any change in the stock
routing of the tubes may pinch the tubes or create low
pressure.
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