Carburetor Tuning - KTM 250 SX 2021 Owner's Manual

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15 TUNING THE ENGINE
15.3
Effects of carburetor tuning
The different carburetor components must be tuned both to one another and for the use intended.
Main jet MJ
The main jet MJ has the greatest influence with the throttle slide open (full throttle).
If the insulator of a new spark plug is very light or white after a brief ride at full throttle, or if the engine knocks, a
larger main jet needs to be used. If the insulator is dark brown or sooty, a smaller main jet needs to be used.
Needle position POS
The needle position has the greatest influence in the mid throttle slide range.
If the engine stutters when accelerating with a partially open throttle slide, the jet needle must be lowered. If the
engine knocks when accelerating at the full power rpm range, the jet needle must be raised.
Cylindrical part of the needle CYL
The cylindrical part of the needle has the greatest influence when the throttle slide is almost closed.
100
400192-11

Carburetor tuning

2
Turn barrel adjuster
so that there is play
cable at the throttle grip.
Guideline
Throttle cable play
3
Tighten nut
.
1
Slide on sleeve
.
Finishing work
Check the throttle grip for smooth operation.
Install the fuel tank.
(
Mount the seat. (
p. 56)
Check throttle cable play. (
A
in the throttle
2 ... 3 mm (0.08 ...
0.12 in)
p. 63)
p. 99)
H01400-01

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2021 2021

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