Filter
Top Products
ENGLISH
32
Carburetor adjustment *
Basic information on the original carburetor setting
The original carburetor setting was adapted for an altitude of approx. 500 meters (1600 ft.) above sea level, and the ambient
temperature of approx. 20° C (68° F), mainly for off-road use and central European premium-grade fuel (95 ROZ).
Mixing ratio (2-stroke motor oil/super fuel): 1:40 (125/144 SX), 1:60 (250 SX)
Basic information on changing the carburetor setting
Always start with the original carburetor setting (the provided factory setting is meant for break-in operation; after the break-in period,
the carburetor needs to be adjusted according to the carburetor datasheet - see appendix). Essential requirements are a clean air fil-
ter system, air-tight exhaust system and an intact carburetor. Experience has shown that adjusting the main jet, the idling jet and the
jet needle is sufficient and that changes of other parts of the carburetor will not greatly affect engine performance.
RULE OF THUMB: high altitude or high temperatures > choose leaner carburetor adjustment
low altitude or low temperatures > choose richer carburetor adjustment
– Only use premium-grade gasoline ROZ 95 (USA = Premium PON 91) mixed with high-grade two-stroke engine oil. Other types of
gasoline can cause engine failure, and will void your warranty.
– Only use high-grade 2-stroke engine oil of known brands (e. g. Motorex Cross Power 2T).
– Not enough oil or low-grade oil can cause erosion of the piston. if you use too much oil the engine can start smoking and foul the
spark plug and the exhaust control system.
– In the case of a leaner adjustment of the carburetor, proceed cautiously. Always reduce the jet size in steps of one number to avoid
overheating and piston seizure.
NOTE: If the engine does not run properly despite a changed adjustment, look for mechanical faults and check the ignition system.
General information on carburetor wear
Engine vibrations subject the throttle slide, jet needle, float needle valve and the needle jet to extreme wear. Wear leads to malfunc-
tioning of the carburetor (e.g. over-enrichment). These parts should be replaced after 100 operating hours. The carburetor body, main
jet holder and the float support should be replaced after 200 operating hours.
MAINTENANCE WORK ON CHASSIS AND ENGINE »
B
C
D
A
idle jet
throttle valve
air control screw
idle adjusting screw
main jet
jet needle
jet needle
Definitions
Mixture too rich:
Too much fuel in proportion to air.
Mixture too lean:
Not enough fuel in proportion to air.
Part-throttle range C
Operation with partly open throttle valve. This range is only influenced by the jet needle (shape and position). The optimum part-throt-
tle setting is controlled by the idling setting in the lower range and by the main jet in the upper range. If the engine runs on a four-
stroke cycle or with reduced power when it is accelerated with the throttle partly open, the jet needle must be lowered by one notch.
If then the engine pings, especially when accelerating under full power at maximum engine revs, the jet needle should be raised.
If these faults should occur at the lower end of the part throttle range at a four-stroke running, make the idling range leaner; if the
engine pings, adjust the idling range richer.
Full throttle range D
Operation with the throttle fully open (flat out). This range is influenced by the main jet and the jet needle. If the porcelain of the new
spark plug is found to have a very bright or white coating or if the engine rings, after a short distance of riding flat out, a larger main
jet is required. If the porcelain is dark brown or black with soot the main jet must be replaced by a smaller one.
Idling range A
Operation with closed throttle valve. This range is influenced by the position
of the air control screw [1] and the air control screw [2]. Only make adjust-
ments when the engine is hot.
To this end, slightly increase the idling speed of the engine by means of the
air control screw. Turning it clockwise produces a higher idling speed and turn-
ing the screw counterclockwise produces a lower idling speed. Create a round
and stable engine speed using the air control screw (basic position of the air
control screw = open by 1.5 turns). Then adjust to the normal idling speed
by means of the air control screw.
Opening up B
Engine behavior when the throttle opens. The idle jet and the shape of the
throttle valve influences this range. If, despite good idling-speed and part-
throttle setting, the engine sputters and smokes when the throttle is fully opened
and develops its full power not smoothly but suddenly at high engine speeds,
the mixture to the carburetor will be too rich, the fuel level too high or the
float needle is leaking.
1
2