Toyota 5R 1969 Repair Manual page 78

p o w e r requires additional rich fuel mixture. H o w e v e r , when the throttle valve
is opened suddenly, the effect is to ''dump" air into the intake manifold, thus
sudd'enly reducing the manifold vacuum. Th is sudden change of air flow , plus
the need fo r a momentary richness of fu el, results inadequate supply of fuel
fo r acceleration
which could cause "flat spot" o r engine lugging, and accelerating system is
incorporated in this carburetor.
When the accelerator pedal is depressed fo r quick acceleration, the plunger
(1 ) connected to the throttle valve is pushed down into the fuel in the pump
cylinder ( 2 ) . Thus the inlet side steel
the outlet side steel ball and the discharge weight (4) , then flows out from
the pump jet (5) to
When the throttle
pump cylinder
period. A ls o when the accelerator pedal is fully d ep ress ed , the p o w e r valve
opens, and the fuel is also supplied from the p o w e r system.
7. Automatic choke system
Th e automatic choke system ope­
rates by the exhaust-manifold temp­
erature, intake-manifold
and the air velocity with the air
h o rn .
a. Starting cold engine
T h e choke valve
close fully at 25 C (77 F ) , th ere­
fo r e , below this temperature, the
choJ<e valve will be closed com ­
pletely .
A s the choke valve is located in
the air horn above the primary b a rr e l, when closed, crea te s a high vacuum.
T h e vacuum causes the fuel to flow from the main fuel system, and also from
the idle and low speed system. T h is supplies a v e r y rich fuel mixture ne­
c e s s a ry to operate a cold engine.
F u l l y c l o s e d
from the main nozzle. T o o v e rc o m e this momentary lapse,
supply the rich
is closed, the pump plunger is pulled upward so that the
becomes refilled
vacuum
is adjusted to
F ig . 5-11 Automatic Choke Operation
F U E L S Y S T E M - Carburetor
ball (3) is closed, and the fuel pushes
mixture n ecessary fo r acceleration.
with fuel, ready fo r the next acceleration
F ig . 5-10
D u r in g w a rm in g - u p
Automatic Choke
System
F u l l y o p e n e d
G0910 , G 09H , G0912
5-9
GO 90 9