KTM 250 EXC 2018 User Manual

17 TUNING THE ENGINE
131
17.3 Carburetor setting
Effects of the carburetor setting
H01400-01
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.
Idling jet IJ
The idling jet has the greatest influence in the low to mid throttle slide range.
If the engine stutters when idling or accelerating with a partially open throttle slide, a smaller idling jet must be
used. If the engine knocks in this power range, then a larger idling jet must be used.
Idle air adjusting screw open ASO
The idle air adjusting screw has the greatest influence during idling.

KTM 250 EXC 2018 Specifications

General

Displacement	249 cm³
Bore x Stroke	66.4 mm x 72 mm
Transmission	6-speed
Fuel System	Carburetor
Cooling	Liquid cooled
Front Suspension	WP Xplor 48 upside-down fork
Rear Suspension	WP Xplor PDS shock absorber
Rear Tire	140/80-18
Front Wheel	1.60 x 21"
Rear Wheel	2.15 x 18"
Ground Clearance	370 mm
Seat Height	960 mm
Engine Type	1-cylinder, 2-stroke
Clutch	Wet multi-disc clutch, hydraulically operated
Frame	Central tube frame made of chrome molybdenum steel
Front Brake	Disc brake
Rear Brake	Disc brake, 220 mm
Front Tire	90/90-21
Starter	Kick and electric starter
Fuel Tank Capacity	9 liters