17 TUNING THE ENGINE 110
The idle speed is adjusted with adjusting screw 1.
The idle mixture is adjusted with the idle air adjusting screw 2.
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Idle air range A
Operation with the throttle slide closed. This range is influenced by adjusting screw 1
and the idle air adjusting screw 2.
Transition range B
Behavior of the engine when the throttle slide is being opened. This range is influenced
by the idling jet and by the form of the throttle slide.
If the engine sputters and smokes heavily when it starts despite a good idle and part-
load setting, and if it abruptly reaches full power at a high rpm, the carburetor setting
is too rich, or the float level is too high or the float needle valve is leaky.
Part-load range C
Operation with the throttle slide partially open. This range is influenced by the jet
needle (form and position). The idle setting influences the engine tuning in the lower
range, and the main jet influences the engine tuning in the upper range.
If, when accelerating with the throttle slide partially opened, the engine only stutters
while running, the jet needle needs to be lowered by one level. If the engine knocks,
especially when it reaches the full performance engine speed while accelerating, the jet
needle needs to be raised. If the behavior described above occurs while idling or just
above idling, the idling system needs to be regulated to a leaner setting if the engine is
stuttering and to a richer setting if knocking.
Full-load range D
Operation with the throttle slide open (full throttle). This range is influenced by the
main jet and jet needle.
If the insulator of a new spark plug is very light or white after a brief ride at full throt-
tle, 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.
17.4 Carburetor - adjusting the idle speed x
B00048-11
– Screw in idle air adjusting screw 2 all the way and turn it to the specified basic
position.
Guideline
Idle air adjusting screw (All 125 models)
Open 2.75 turns
Idle air adjusting screw (All XC-W models)
Open 2.0 turns
Idle air adjusting screw (200 EXC EU)
Open 1.5 turns
Idle air adjusting screw (200 EXC AUS)
Open 1.0 turn
Idle air adjusting screw (250/300 EXC AUS)
Open 3.5 turns
Idle air adjusting screw (250 EXC EU, 250 EXC SIX DAYS EU)
Open 1.5 turns
Idle air adjusting screw (300 EXC EU, 300 EXC SIX DAYS EU)
Open 1.75 turns
– Run the engine until warm.
Guideline
Warm-up time ≥ 5 min
Danger
Danger of poisoning Exhaust gases are toxic and inhaling them may result
in unconsciousness and/or death.
– When running the engine, always make sure there is sufficient ventila-
tion, and do not start or run the engine in an enclosed space without an
effective exhaust extraction system.
– Adjust the idle speed with adjusting screw 1.
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