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Table of Contents
1982 AND LATER SERVICE INFORMATION
267
CHAPTER SEVEN
FUEL AND EXHAUST SYSTEMS
New carburetor specifications for the
KZ550-H1 and KZ550-F1 and M1 models
are found in Table 16 and Table 17.
Carburetor specifications for the ZX550-A1
and A2 are found in Table 18. These models
use constant-velocity type carburetors as
explained in the following paragraphs.
CARBURETOR OPERATION
(CONSTANT-VELOCITY TYPE)
The following paragraphs explain the basic
operation of carburetors, which may be
helpful in troubleshooting a problem you
suspect is caused by carburetion. If you are
disassembling a carburetor,
go on to
Carburetor Service
in this section of the
supplement.
The constant-velocity carburetor has a
rotating butterfly throttle valve and an engine
vacuum-controlled sliding valve that cames
the jet needle. This type of carburetor is less
susceptible than some caburetors to a stall in
acceleration when the throttle is snapped
open, because the vacuum slide will not rise
until gradually increasing engine vacuum
pulls it up. The constant-velocity carburetor
is also not as sensitive to changes in altitude
as some carburetors are.
Vacuum Slide
The vacuum slide position is controlled by
a diaphragm that has engine vacuum on top
and atmospheric pressure on the bottom. The
slide moves up and down with engine
vacuum; any change in atmospheric pressure
(such as a change in altitude) also moderates
the slide position slightly to maintain a
constant air-fuel ratio. The vacuum slide
affects the fuel mixture from 1/4 to 3/4
throttle.
Pilot and Primary
Main Fuel Systems
NOTE
This description describes carburetor
operation at a steady speed. When
accelerating, the vacuum slide lags
behind the throttle valve.
The carburetor's purpose is to supply and
atomize fuel and mix it in correct proportions
with air that is drawn in through the air
intake. At primary throttle openings (from
idle to 1/8 throttle), a small amount of fuel is
siphoned through the pilot jet by suction from
the incoming air. As the throttle is opened
further (from 1/4 to 1/2 throttle), the vacuum
slide begins to rise and the air stream also
begins to siphon fuel through the primary
main jet. From 1/2 to 3/4 throttle, the
vacuum slide continues to rise and fuel also
siphons through the needle jet. The tapered
needle allows the needle jet to flow more fuel
as the needle rises with the vacuum slide.
From 3/4 to full throttle, the vacuum slide is
fully open and fuel siphons through the
secondary main jet and needle jet. At full
throttle, the needle is lifted far enough to
permit the secondary main jet to flow at full
capacity.
CARBURETOR TROUBLESHOOTING
(CONSTANT-VELOCITY TYPE)
Diagnosing the Problem
In addition to the items listed in the main
book, if the engine won't rev to high rpm,
check for a hole in the vacuum diaphragm.
CARBURETOR VARIABLES
(CONSTANT-VELOCITY TYPE)
The following parts of the carburetor can be
changed to alter the fuel mixture. Each part
has the most effect over a narrow range of
throttle openings, but each also has a lesser
effect over a broader range of throttle
openings.
Pilot Jet and Screw
The pilot jet and idle mixture setting affect
mixture from 0 to about 1/8 throttle. As pilot
jet numbers increase, the fuel mixture gets
richer. As the idle mixture (pilot air) screw is
opened (turned out), the mixture gets leaner.
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