16
TUNING THE ENGINE
84
16.3
Carburetor - idle
L00927-10
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.
(125/150 SX)
Elevation above sea level
500 m (1,640 ft)
Ambient temperature
20 °C (68 °F)
Super unleaded gasoline (98 octane), mixed with 2-stroke engine oil (1:40)
(All 250/300 models)
Elevation above sea level
500 m (1,640 ft)
Ambient temperature
20 °C (68 °F)
Super unleaded gasoline (95 octane), mixed with 2-stroke engine oil (1:60)
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, 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 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 above events occur on idle or
just above it, the idle system must be set to a leaner setting if the engine is stuttering
or to a richer setting if the engine is 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-colored 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.
16.4
Carburetor - adjusting the idle speed
x
L00927-10
–
Screw in idle air adjusting screw
all the way and turn it to the specified basic
position.
Summary of Contents for 125 SX EU 2015
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