15 TUNING THE ENGINE 72
15.3 Carburetor - idle
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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 carburetor's factory setting matches the following values.
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. 88)
500282-01
Idling range A
Operation when throttle side is closed. This range is affected by adjusting screw
and idle air adjusting screw
.
Transitional range B
Engine behavior when the throttle slide is opened. This range is affected by the idling
jet and throttle slide.
If, despite good idling and part-load settings, the engine starts to stutter and smoke
heavily when the throttle slide is opened, and if it reaches full performance at high
engine speeds suddenly, the carburetor is not being regulated leanly enough, the float
level is too high or the float needle valve is leaky.
Part-load range C
Operation when throttle side is partially open. This range is affected by the jet needle
(shape and position). In the lower range, the idle setting affects engine tuning; in the
upper range, it is the main jet.
If, during acceleration with a partially opened throttle slide, the engine runs only at
stuttering performance, the jet needle must be lowered by one notch. If the engine
knocks, particularly during acceleration, when it is in the top-performance engine
speed range, the jet needle must be raised. If the phenomena described above occur
during idling or just above, the idling system is to be regulated more leanly during
stuttering performance, and less so during knocking.
Full-load range D
Operating with open throttle slide (full throttle). This range is affected by the main jet
and the jet needle.
If the insulator of a new spark plug is very bright or white after a short journey at full
throttle, or if the engine is knocking, a larger main jet must be used. If the insulator is
dark brown or sooty, a smaller main jet must be used.
15.4 Carburetor - adjusting idle speed
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–
Screw in idle air adjusting screw
all the way and turn it to the specified basic
position.
Guideline
Idle air adjusting screw
Open 1.5 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 death.
– Always make sure there is sufficient ventilation when running the
engine.
– Use an effective exhaust extraction system when starting or running the
engine in an enclosed space.
–
Adjust the idle speed with adjusting screw
.
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