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43
MAINTENANCE WORK ON CHASSIS AND ENGINE
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Definitions
Mixture too rich:
Too much fuel in proportion to air.
Mixture too lean:
Not enough fuel in proportion to air.
Idling range A
Operation with closed throttle valve. This range is influenced by the position
of the air control screw [2] and the air control screw [3]. 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.
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-throttle 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 dis-
tance 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.
B
C
D
A
idle jet
throttle valve
air control screw
idle adjusting screw
main jet
jet needle
jet needle
1
2
Explanation of table - Example
Compared to the needle NOZI, the jet needle NOZG is two steps leaner in
the range from the closed position of the throttle to 1/4 throttle. Otherwise,
there are no differences.
Pay attention to the correct needle designation when replacing the jet nee-
dle. detailed information on the type of jet needle for the respective models
can be found in the carburetor setting table.
JET NEEDLE
TYPE
RANGE OF ACTION
RICHER LEANER
NOZD
NOZE
NOZF
NOZG
NOZH
NOZI
JET NEEDLE
TYPE
RANGE OF ACTION
RICHER LEANER
N8RG
N8RH
N8RW
N8RJ