I I I - Yamaha SL292C 1971 Service Manual

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ENGINE MAINTENANCE -
Carburetion and Fuel System
fuel pump chamber. Then, the fuel continues to fl ow
through the outlet check valve and inlet control valve into
the regulator chamber .
When the fuel flows into the regulator chamber, the main
diaphragm is given a downward force, ar1d at the
sarT1e
time, the diaphragm control lever is moved d own at the
one end and moved up at the other end . Tl1is causes t l1e
inlet control valve (needle) to move up to its closed
position and stops the flow of fuel into the regulator
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chamber.
As the
fuel level loweres, the pressure against the main
diaphragm decreases and the main diaphragm spring over-
comes the force of the inlet tension spring, thus pushir1g
up the inlet control lever at the one end . This causes the
inlet control lever to move down at the other end, and
allows the inlet control valve to move down. At this
movement, the fuel begins to flow in . This is. as the fu el
lever in the regulator chamber lowers, the inlet control
valve opens. On the contrary, as the fuel level rises, the
inlet control valve begins to close .
In this way, the balance between the main diaphragm
spring tension and the inlet tension spring tension ma in-
tains the fuel level constant, and the fuel is fed to the
engine . At low speed, the fuel is drawn into the engine
through the idle discharge port alone.
With
1 /4
throttle or rriore, the fuel is drawn t hrough the
main discharge port and fully atomi zed in the primary
venturi, being supplied to the engine .
The fuel is controlled by the slow adjusting screw at low
speed and by the main adjusting screw at high speed at a
proper rate according to fuel consumption in the engine.
2.
To remove the carburetor, disconnect fuel line, pressure
pulse line, disconnect the pump operating rod and then
loosen the carburetor from the cylinder.
Cleaning of the carburetor and any carburetor parts
should be done in
clean gasoline on solvent . After any
dirt of film build-up has been removed, all parts should
be blown off with an air hose .
Fig. 8-11
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Crank case
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Cylinder
Carburetor
~g;-:;-Pressure
pulse line
.-:/ Primer pump
Fuel line
Fuel tank
Vent
3 . Carburetor Setting
All carburetors are subject t o stri ct testing befo re sliip-
ment. Tt1erefore. no attem pt to tou ct1 t t1e adjus ted po ints
should be made ur1n ecessarily, o tl1erwise t l1e per formar1 ce
of tl1e carburetor will be ir11paired. It t l1e carb uretor is
cl1ecked, cleaned or disassembled for replacemen t o f
parts, or used LJnder special at rnospheric conditio ns, or at
altitude. tl1e followi 1 1g procedures r11ust be foll owed w ith
special care f or readj ustn1ent . Tt1e adjustment po in ts are
three places as fo llows:
1. Slow ad justi1 1g screw co ntrolling the ai r-fuel m ixture
at idling speed .
2. Idle speed screw (throttle stop screw) control ling the
id Ii ng speed.
3. Main adjusting screw controlling the ai r-fuel mixture
wl1ile the throttle st1 utter is post 1 /4 tl1rottl e.
The setting is done with the consideration that the
snovvmobi le is used in winter at low altitL1d e. If tl1e
snowm ob ile is operated at high altitudes or under specia l
atn1ospheric conditions, t l1e specified setting may not be
suitable. Accordingly, t he ca rb uretor may be readjusted
so that its performance will be maxirnum . It shou ld be
pointed out th at, in general, t he carburetors, both right
and left, should be even ly adjusted .
The adjust scr ew shou ld be turned out frorn a I ightly
seated position accordi ng to the following tabl e.
Number of t ur ns to be backed off.
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Fig. 8-12
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Throttle
stop sc rew
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Fig . 8-13
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