16 TUNING THE ENGINE 98
– Check the play in the throttle cable. ( p. 97)
16.3 Carburetor – idle
M01173-10
The idle setting of the carburetor has a big influence on the starting behavior, stable
idling, and the response to throttle opening. This means that an engine with a correctly
set idle speed is easier to start than if the idle is set wrongly.
Info
The carburetor and its components are subject to increased wear caused by
engine vibration. Wear can result in malfunctioning.
The factory setting for the carburetor is set for the following values.
(All 125/150 models)
Height above sea level 500 m (1,640 ft)
Ambient temperature 20 °C (68 °F)
Super unleaded (98 octane) mixed with 2-stroke engine oil (1:40) ( p. 135)
(All 250/300 models)
Height above sea level 500 m (1,640 ft)
Ambient temperature 20 °C (68 °F)
Super unleaded (95 octane) mixed with 2-stroke engine oil (1:60) ( p. 135)
The idle speed is adjusted with adjusting screw
.
The idle mixture is adjusted with the idle air adjusting screw
.
500282-01
Idle air range A
Operation with the throttle slide closed. This range is influenced by adjusting screw
and the idle air adjusting screw
.
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, 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 the engine stutters when accelerating with a partially open throttle slide, the jet nee-
dle must be lowered by one notch. If the engine knocks when accelerating at the full
power rpm range, the jet needle must be raised. If the phenomena described above
occur during idling or just above, the idling system must be regulated more leanly dur-
ing stuttering and less so during 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.
16.4 Carburetor – adjusting the idle speed
M01173-11
–
Screw in idle air adjusting screw
all the way and turn it to the specified basic
position.
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