KTM 250 SX - Manual (Page 17)

2-3C
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
temperature of approx. 20° C (68° F), mainly for off-road use and central European premium-grade fuel (ROZ 95 MOZ). Mixing
ratio 2-stroke motor oil : super fuel 1:40 – 1:60.
Basic information on a change of the carburetor setting
Always start out from the original carburetor setting. 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 ➞ choose leaner carburetor adjustment
low altitude or low temperatures ➞ choose richer carburetor adjustment
ƽ WARNING ƽ
– O NLY USE PREMIUM - GRADE GASOLINE ROZ 95 MIXED WITH HIGH - GRADE TWO - STROKE ENGINE OIL . O THER TYPES OF GASOLINE CAN CAUSE ENGINE
FAILURE , AND USE OF SAME WILL VOID YOUR WARRANTY .
– O NLY USE HIGH - GRADE 2- STROKE ENGINE OIL OF KNOWN BRANDS .
– N OT ENOUGH OIL OR LOW - GRADE OIL CAN CAUSE EROSION OF THE PISTON . U SING TOO MUCH OIL , THE ENGINE CAN START SMOKING AND FOUL THE
SPARK PLUG .
– I N THE CASE OF A LEANER ADJUSTMENT OF THE CARBURETOR PROCEED CAUTIOUSLY . A LWAYS REDUCE THE JET SIZE IN STEPS OF ONE NUMBER TO AVOID
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
carburetor malfunction (e.g., overly rich mixture). Therefore, these parts should be replaced after 10000 kilometers (6000 miles).
Explanation - Example
Compared to the needle N 85 A, the jet needle N 85 C is two steps leaner
in the range from the closed position of the throttle to 1/4 throttle.
Otherwise, there are not differences.
! CAUTION !
W HEN CHANGING THE JET NEEDLE , MAKE SURE THAT YOU USE THE CORRECT NEEDLE
TYPE (N 85 ,NOZ OR N3). T HE TECHNICAL DATASHEET TELLS YOU WHICH JET
NEEDLE CAN BE USED FOR WHICH MODEL .
N 85 C 0 – 1 /
4
ࠗ – ࠗ –
jet needle throttle valve open effect
N 85 A
N 85 B
0 – 1 / 4
ࠗ –
N 85 C 0 – 1 /
4
ࠗ – ࠗ –
N 85 D 0 – 1 /
4
ࠗ – ࠗ – ࠗ –
N 85 E 0 – 1 /
4
ࠗ – ࠗ – ࠗ – ࠗ –
NOZ C
NOZ D
0 – 1 /
4
ࠗ –
NOZ E 0 – 1 /
4
ࠗ – ࠗ –
NOZ F 0 – 1 /
4
ࠗ – ࠗ – ࠗ –
NOZ G 0 – 1 / 4
ࠗ – ࠗ – ࠗ – ࠗ –
NOZ H 0 – 1 /
4
ࠗ – ࠗ – ࠗ – ࠗ – ࠗ –
NOZ I 0 – 1 /
4
ࠗ – ࠗ – ࠗ – ࠗ – ࠗ – ࠗ –
NOZ J 0 – 1 /
4
ࠗ – ࠗ – ࠗ – ࠗ – ࠗ – ࠗ – ࠗ –
N3CG
N3CH
0 – 1 /
4
ࠗ –
N3CW 0 – 1 /
4
ࠗ – ࠗ –