3. 6 CARBURETOR
However, if the operation is improper, fuel is
excessively fed to the engine, and the engine stops.
For this reason, relief valve (181 is provided on
the choke valve (31. The relief valve ( 181 opens
and closes by the inhale negative pressure, and
makes the mixture suitable to a cold engine.
Thus, fully opening the choke valve (31, warm-up
operation can be continued. (Fig. 3. 128)
B. Carburetor Adjustment
l. Idling ( Fig. 3. 131)
When idling, the throttle valve ( 151 is in an
almost closed position, and the fuel is jetted from
the pilot outlet 1121. Accordingly, the mixture reg-
ulation is performed at the pilot screw. When the
pilot screw is turned in, the mixture becomes rich,
and becomes rich when the screw is turned out.
The pilot screw should be set at a point l
~
1
1
/
4
of a turn out from full close.
The engine rpm at idling point is between l 000 -
1200 rpm. (Fig. 3. 129)
2. Low and Cruising Speeds. (Fig. 3. 131-b)
The fuel is mainly jetted from the by pass ( l 31
because the throttle valve ( 15) is opened in at a
specific level. Accordingly, the mixture adjustment
is set by the inside diameter of the slow jet.
3. Medium Speed (Fig. 3. 131-c)
The opening of the throttle valve ( 151 becomes
larger, the vacuum piston ( 16) starts rising, and
the fuel starts to jet from the needle jet; however,
the jetting value is requlated by the jet needle.
Accordingly, the mixture adjustment is performed
by the setting position of the jet needle to the
vacwm piston (1 61.
Fig. 3. 128 Relief valve
Fig. 3.
129 Pilot screw
Fig. 3. 130 Jet needle
61
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