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KTM LC4 400-660LC42003 engine. Manual - part 18

7-51D

Checking the speedometer sensor and the speedometer
(Adventure – from the 2002 model)

Checking the speedometer:

– Disconnect the connector

from the speedometer.

NOTE: The connector

is located under the cockpit covering.

– Switch on the ignition.
– Briefly connect pins

and

(cable colors black/brown and

black/orange) with a cable several times while you observe the speed
reading. If the speedometer is functioning correctly, the speed should
be indicated.

Checking the speedometer sensor:

NOTE: The measurement must be made with the ignition switched on
and the plug and socket connection connected.

– Use a digital multimeter to measure the voltage at the black cable on

connector

against the ground.

– Slowly turn the front wheel.
– The measured value should be over 4.5 volts when the wheel is

turned or less than 1 volt when the magnet on the front-wheel hub
is within the range of the speed sensor.

CAUTION

INCE YOU MUST MEASURE WITH THE CONNECTOR ATTACHED

MAKE SURE TO

CAREFULLY PUSH THE MEASURING TIPS ON THE MULTIMETER THROUGH THE SEALING
FROM THE CABLE SIDE AND NOT TO DAMAGE ANY PART OF THE CONNECTOR

Repair manual KTM LC4

Art.-Nr

. 3.206.006 -E

FUEL SYSTEM

MIKUNI BST 40
PART-LOAD SYSTEM  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-4
FULL-LOAD SYSTEM  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-5
DISASSEMBLING THE CARBURETOR  . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-6
ASSEMBLING THE CARBURETOR  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-8
CHECKING/ADJUSTING THE THROTTLE SENSOR  . . . . . . . . . . . . . . . . . . .8-9
ADJUST IDLING SPEED  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-10
ADJUSTING THE THROTTLE CABLE  . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-10
CHECK FLOAT LEVEL  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-10

DELL’ORTO
DISASSEMBLING THE CARBURETOR (DELL’ORTO PHM 40 SD)  . . . . . . .8-12
ASSEMBLING THE CARBURETOR (DELL’ORTO PHM 40 SD)  . . . . . . . . . .8-13
DISASSEMBLING THE CARBURETOR (DELL’ORTO PHM 38 ND)  . . . . . . .8-16
ASSEMBLING THE CARBURETOR (DELL’ORTO PHM 38 ND) . . . . . . . . . .8-18
DISASSEMBLING THE CARBURETOR (DELL’ORTO VHSB 38 QS)  . . . . . . .8-21
ASSEMBLING THE CARBURETOR (DELL’ORTO VHSB 38 QS)  . . . . . . . . .8-22
CHECK FLOAT LEVEL (DELL’ORTO 38 ND / 40 SD)  . . . . . . . . . . . . . . . . .8-25
CHECKING AXIAL CLEARANCE OF FLOAT (DELL’ORTO 38 ND / 40 SD)  . .8-25
ADJUST HOT START DEVICE (DELL’ORTO 40 SD)  . . . . . . . . . . . . . . . . . .8-25
ADJUSTING THE THROTTLE CABLE  . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-26
ADJUSTING THE CHOKE CABLE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-26

KEIHIN FCR 41
DISASSEMBLING THE CARBURETOR  . . . . . . . . . . . . . . . . . . . . . . . . . . .8-28
CHECKING THE CHOKE SLIDE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-31
CHECKING THE ACCELERATOR PUMP  . . . . . . . . . . . . . . . . . . . . . . . . . .8-31
CHECKING THE JET NEEDLE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-31
CHECKING THE FLOAT NEEDLE VALVE  . . . . . . . . . . . . . . . . . . . . . . . . . .8-31
CHECKING THE THROTTLE VALVE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-31
ASSEMBLING THE CARBURETOR  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-32
ADJUSTING THE POSITION OF THE THROTTLE VALVE SENSOR  . . . . . . .8-35
CHECKING THE THROTTLE VALVE SENSOR  . . . . . . . . . . . . . . . . . . . . . .8-36
DISMOUNTING AND INSTALLING THE THROTTLE VALVE SENSOR  . . . . .8-36
ADJUST IDLING SPEED  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-37
CHECKING/ADJUSTING THE FLOAT HEIGHT  . . . . . . . . . . . . . . . . . . . . .8-38

INDEX

8-1D

8-2D

Repair manual KTM LC4

Art.-Nr

. 3.206.006 -E

KEIHIN FCR-MX 41
DISASSEMBLING THE CARBURETOR  . . . . . . . . . . . . . . . . . . . . . . . . . . .8-40
CHECKING THE CHOKE SLIDE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-43
CHECKING THE ACCELERATOR PUMP  . . . . . . . . . . . . . . . . . . . . . . . . . .8-43
CHECKING THE JET NEEDLE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-43
CHECKING THE FLOAT NEEDLE VALVE  . . . . . . . . . . . . . . . . . . . . . . . . . .8-43
CHECKING THE THROTTLE VALVE  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-43
ASSEMBLING THE CARBURETOR  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-44
ADJUSTING THE POSITION OF THE THROTTLE VALVE SENSOR  . . . . . . .8-47
CHECKING THE THROTTLE VALVE SENSOR  . . . . . . . . . . . . . . . . . . . . . .8-48
DISMOUNTING AND INSTALLING THE THROTTLE VALVE SENSOR  . . . . .8-48
ADJUST IDLING SPEED  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-49
CHECKING/ADJUSTING THE FLOAT HEIGHT  . . . . . . . . . . . . . . . . . . . . .8-49

INDEX

Repair manual KTM LC4

Art.-Nr

. 3.206.006 -E

8-3D

CARBURETOR - MIKUNI BST 40

Part-load system (Mikuni BST 40)

The part-load system supplies the engine with fuel while the throttle slide is closed or only slightly
opened.

From the float chamber the fuel enters the mixture pipe through the idling jet. There the fuel
mixes with the air that flows in through the idling air jet.
Then the fuel air mixture reaches the idle adjusting screw and the bypass bores through the
mixture pipe.
A certain amount of the fuel air mixture is sucked into the intake pipe through the bypass bores.
The remaining fuel air mixture is adjusted by the idle adjusting screw and enters the intake pipe
through the idling bore.

8-4D

AIR

FUEL AIR MIXTURE

FUEL

Repair manual KTM LC4

Art.-Nr

. 3.206.006 -E

Full-load system (Mikuni BST 40)

When the throttle valve is opened the engine speed increases and the negative pressure in the
venturi pipe grows. The same negative pressure is transferred to the upper side of the slide
membrane and pulls the throttle slide upwards.
At the same time the fuel flows from the float chamber through the main jet into the needle jet.
There it mixes with the air flowing in through the main air jet. The result is a fuel air mixture.
Negative pressure causes this fuel air mixture to flow through the space between the needle jet
and the jet needle into the venturi pipe. There it meets the main air flow sucked in by the
engine.

The precise amount of the mixture released is adjusted in the needle jet. The space through which
the mixture passes changes depending on the position of the throttle slide.

Throttle slide in top position: large space

Throttle slide in bottom position: small space

8-5D

AIR

FUEL AIR MIXTURE

FUEL

8-6D

Disassembling the carburetor (Mikuni BST-40)

NOTE: Before commencing to disassemble the carburetor make sure
that your workplace is clean and large enough to properly arrange all
carburetor components before you.

CAUTION

O PREVENT DAMAGING OF THE SLIDE MEMBRANE DO NOT APPLY COMPRESSED AIR

TO CLEAN THE CARBURETOR BEFORE REMOVING THE MEMBRANE

– Remove the two screws

and take off the membrane cover.

– Remove the throttle stop.

– Take the throttle slide out of the carburetor together with the spring.

– Pull the jet needle

out of the throttle slide.

– Remove the 2 screws

and take off the float chamber together

with the gasket.

Repair manual KTM LC4

Art.-Nr

. 3.206.006 -E

8-7D

– Take the entire float unit

out of the carburetor.

– Then remove the main jet

together with the distance bushing.

– Remove the idling jet

– Twist the mixture adjusting screw

clockwise all the way in. Count

and write down the number of twists.
Twist out the mixture adjusting screw and remove it together with
the spring, the O-ring and the washer.

– Use a screwdriver to push the needle jet

upwards out of the

carburetor.

– Clean all jets and blow them through with compressed air.
– Clean the carburetor housing and use compressed air to blow through

all ducts within the carburetor.

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