KTM 400-660 LC4 1998-2005, Repair Manual

Page: 213 / 501

8-49E
Repair manual KTM LC4
Art.-Nr
. 3.206.014 -E
CARBURETOR – Adjust idling (Keihin FCR-MX 41)
Idling adjustment of the carburetor strongly affects the engine’s starting
behavior. That is, an engine whose idling speed is adjusted correctly will
be easier to start than one whose idling speed has not been adjusted
correctly.
The idle speed is controlled by means of the adjusting wheel
1
and the
mixture control screw
2
. The adjusting wheel is used to adjust the basic
setting of the slide. The mixture control screw is used to control the idle
mixture which arrives at the engine by way of the idle system.
Clockwise turning reduces the fuel quantity (lean mixture),
counterclockwise turning increases the fuel quantity (rich mixture).
TO ADJUST IDLING CORRECTLY, PROCEED AS FOLLOWS:
1 Turn in mixture control screw
2
up to the stop, and turn it back out
to the basic position (see technical date-engine)
2 Warm up the engine
3 Use the adjusting wheel
1
to set the normal idle speed (1400 -
1500 rpm).
4 Turn mixture control screw
2
slowly clockwise until idling speed
starts to decrease. Memorize this position, and turn mixture control
screw slowly counterclockwise until the idling speed decreases again.
Adjust the point of the highest idling speed between these two
positions. If, in the course of this procedure, the speed undergoes a
relatively high increase, reduce the idle speed to a normal level and
repeat the procedure specified in 4. Serious competitive racers will
choose a setting approx. 1/4 turn (clockwise) leaner than this ideal
value because their engine will heat up more when used in
competitions.
NOTE: If you fail to obtain a satisfying result by following the
procedure described above, an incorrectly dimensioned idling nozzle
may be the cause. If:
a) the mixture control screw has been screwed in up to the stop
without causing any change in rotational speed, a smaller idling jet
has to be installed;
b) the engine dies when the mixture control screw is still open by
2 turns, a larger idling jet needs to be selected.
Naturally, in cases of jet changes, you have to start your adjusting
work from the beginning.
5 Then, use the adjusting wheel to set the desired idle speed.
6 In cases of greater changes in the outside temperature and extremely
different altitudes, the idling speed should be readjusted.
Basic information on carburetor wear
As a result of engine vibrations, the throttle valve, jet needle, and
needle jet are subjected to increased wear. This wear may cause the
carburetor to malfunction (e.g., overly rich mixture). Therefore, these
parts should be replaced after 200 hours.
Adjusting the mixture control screw
Especially on the EXC models, accessing the mixture control screw is
difficult. For this reasons, we have created an appropriate special tool.
Introduce the special tool on the mixture control screw 2 at the
carburetor bottom. Press the tool slightly upward and turn the adjusting
wheel
3
until the tool engages the slot of the mixture control screw.
Now, you can go about adjusting the screw. Marks were provided on
the adjusting wheel, making it easier to keep track of the turns.
Checking the float level (float height)
For this purpose, dismount the carburetor and remove the float
chamber. Hold the carburetor in a slanted position such that the float
will abut the float needle valve but not compress it.
In this position, the edge of the float should be parallel with the
float chamber sealing surface (see illustration).
If the float height does not correspond to the desired value, check the
float needle valve and, if necessary, replace it.
If the float needle valve is o.k., you can adjust the float height by
bending the float lever
4
.
Mount the float chamber, install the carburetor, and adjust the idle
speed.
2
4
1
3