Suzuki Intruder 1978 Service Manual page 37

•
Throttle Slide
The amount of air entering the carburetor is deter -
mined by the throttle slide . The throttle slide rides
in a closely fitting bore directly above the venturi in
the carburetor body. The movement of the slide is
cont rolled by a cable and spring . In the " fully
closed" position, little or no space remains under
the slide for the air to flow through the venturi . As
the slide is raised higher, more air will flow
through the venturi and into the engine . When the
slide is in a lower position, it blocks part of the
venturi, and the area under the slide becomes a
venturi in a venturi . The size of the actual venturi
or air passage changes with the position of the
slide . This is known as a variable venturi type. It is
the most common type found on snowmobiles and
is used on all Kawasaki s.
At lower throttle pos itions, the cutaway of the
throttle slide affects mixture ratios . The effect of
the cutaway is felt most from about 1/ 8 to 1/ 3
throttle . The higher the cutaway, the leaner the
mixture will be at a constant throttle position. The
higher cutaway offers less resistance to the in -
coming air. The fuel supply rema ins relatively con -
stant at any constant throttle position, and the
additional air results in a leaner mixture . The lower
the cutaway, the greater air flow resistance, and a
richer mixture . The slide cutaway provides for
adjustment of the fuel / air ratio as the transition is
made from idle to the full venturi action of the
carburetor. (See Figure 2-20.)
t
CUTAWAY
+
Figure 2-20
Main System
Four separate systems meter the fuel and mix it
with the air : The main system for normal running ,
the pilot system for low speed running , the econo
jet system for addit ional fuel requirements during
full throttle operation, and the starter system to
assist starting with a cold engine .
The largest portion of the meter ing is performed by
the main system. The components are: The throttle
slide, jet needle , need le j et, and the main jet. As
soon as there is enough air flow through the
venturi to draw fu el up into the main jet/ needl e jet
assembly, the main system takes effect . Th e main
system components meter f uel from 1/ 8 throttle to
full throttle . The throttle slid e is pa rt of th e m ain
system only in that it carri es the jet needle .
OVERALL
LENGTH
Figure 2 -21
FIRST TAPER
SECOND TAPER
The jet needle rides in the throttle slide and moves
up and down with the slide . The needle itself is
tapered at its lowe r end and has grooves at its top
end . Figure 2-21 shows a typical double taper jet
needle. The needle is tapered in two stages . This
double taper needle is used in larger two -stroke
engines . The markings on a needle indicate the
length of the needle and the taper of both sec -
THEORY OF OPERATION 2-17