TUNING THE ENGINE 16
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16.3
Carburetor tuning
Effects of carburetor tuning
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 at idle speed or when 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 at idle speed.
