Carburetor Adjustment - KTM 125SX Owner's Handbook Manual

Carburetor adjustment *

Basic information on the original carburetor setting
The original carburetor setting was adapted for an altitude of approx. 500 meters (1600 ft.) above sea level, and the ambient tempe-
rature of approx. 20° C (68° F), mainly for off-road use and central European premium-grade fuel (95 ROZ).
Mixing ratio (2-stroke motor oil : super fuel)
Basic information on a change of the carburetor setting
Always start with the original carburetor setting (the provided factory setting is meant for break-in operation; after the break-in
period, the carburetor needs to be adjusted according to the carburetor datasheet - see appendix). Essential requirements are a clean
air filter system, air-tight exhaust system and an intact carburetor. Experience has shown that adjusting the main jet, the idling jet and
the jet needle is sufficient and that changes of other parts of the carburetor will not greatly affect engine performance.
RULE OF THUMB: high altitude or high temperatures
low altitude or low temperatures
– O -
NLY USE PREMIUM GRADE GASOLINE
,
FAILURE AND USE OF SAME WILL VOID YOUR WARRANTY
– O - 2-
NLY USE HIGH GRADE STROKE ENGINE OIL OF KNOWN BRANDS
– N -
OT ENOUGH OIL OR LOW GRADE OIL CAN CAUSE EROSION OF THE PISTON
SPARK PLUG AND THE EXHAUST CONTROL SYSTEM
– I
N THE CASE OF A LEANER ADJUSTMENT OF THE CARBURETOR PROCEED CAUTIOUSLY
OVERHEATING AND PISTON SEIZURE
NOTE: If despite a changed adjustment the engine does not run properly, look for mechanical faults and check the ignition system.
Basic information on carburetor wear
As a result of engine vibrations, throttle valve, jet needle, and needle jet are subjected to increased wear. This wear may cause carbu-
retor malfunction (e.g., overly rich mixture). Therefore, these parts should be replaced after 10000 kilometers (6000 miles).
2
1:40 – 1:60
WARNING
ROZ 95
MIXED WITH HIGH
.
(i. e. Shell Advance Racing X).
.
.
Definitions
Mixture too rich:
Too much fuel in proportion to air.
1
Mixture too lean:
Not enough fuel in proportion to air.
Idling range
Operation with closed throttle valve. This range is influenced by the posi-
tion of the air control screw
adjustments when the engine is hot.
To this end, slightly increase the idling speed of the engine by means of the
air control screw. Turning it clockwise produces a higher idling speed and
turning the screw counterclockwise produces a lower idling speed. Create a
round and stable engine speed using the air control screw (basic position of
main jet
the air control screw = open by 1.5 turns). Then adjust to the normal idling
jet needle
speed by means of the air control screw.
jet needle
Opening up
Engine behavior when the throttle opens. The idle jet and the shape of the
idle jet
throttle valve influences this range. If, despite good idling-speed and part-
throttle valve
throttle setting, the engine sputters and smokes when the throttle is fully
opened and develops its full power not smoothly but suddenly at high
air control screw
engine speeds, the mixture to the carburetor will be too rich, the fuel level
idle adjusting screw
too high or the float needle is leaking.
(depands on oil quality)
©
choose leaner carburetor adjustment
©
choose richer carburetor adjustment
- -
GRADE TWO STROKE ENGINE OIL
. U ,
SING TOO MUCH OIL
. A
LWAYS REDUCE THE JET SIZE IN STEPS OF ONE NUMBER TO AVOID
A
1
B
. O
THER TYPES OF GASOLINE CAN CAUSE ENGINE
THE ENGINE CAN START SMOKING AND FOUL THE
2
and the air control screw
29
. Only make