open bonnet DATSUN 610 1969 Workshop Manual

Fuel

System

DESCRIPTION

FUEL
TANK

FUEL
PUMP

CARBURETTOR
IDLING
ADJUSTMENT

FAST
IDLE
OPENING
ADJUSTMENT

THROTTLE
VALVES
INTERLOCK
OPENING

DASHPOT

DESCRIPTION

The

diaphragm
type
fuel

pump
shown
in

Fig
D
1
feeds

fuel

from
the
tank
to
the
carburettor
in
a

regulated
supply

according
to
the
needs
of
the

engine
A
cartridge
type
fuel

strainer

prevents
any
dirt
from

reaching
the

pump
inlet
valve

The

carburettor
fitted
to

the

engine
is
either
a
down

draught
two
barrel

type
equipped
with
a
throttle

operated

acceleration

pump
and
power
valve
mechanism

See
Fig
D
2

or
a
twin
SU
carburettor
of
the

type
shown
in

Fig
D
3
In
the

two
barrel

type
carburettor

fuel
flows
from
the

passage
at
the

bottom
of
the
float
chamber

passes
through
the

primary
main

jet
and
mixes
with
air

introduced

through
the
main
air
bleed

screw

The

petrol
and
air
mixture
is

injected
into
the
venturi

through
the
main
nozzle

Each
time
the
accelerator

pedal
is

depressed
the
throttle

opens
and
the
accelerator

pump
forces
a

jet
of

petrol
into
the

air
stream
to
allow
the

engine
to
accelerate

smoothly
See

Fig

0
4
The

power
valve
mechanism
is

operated
automatically

according
to
the
demands
made

by
the

engine
Under
light
load

i
e

part
throttle
conditions
the
intake
manifold

depression
is

transmitted
below
the
throttle
valve
the
vacuum

pulls
a

piston

upwards
against
a

spring
and
leaves
the

power
valve
closed

allowing
additional
air
to
be

admitted
through
the
air
bleed
screw

and
thereby
weaken
the

petrol
and
air
mixture
When
the
vacuum

below
the
throttle
vaJve
is
lowered

during
full
load
conditions

the

piston
is

pushed
down
opening
the

power
valve
and
providing

additional
fuel
to
enrichen
the
mixture

The
model

HJ
L
38W6
SU
twin
carburettor
is
of

the

horizontal
variable
venturi

type
and
is
used

only
on
the
1600

and
1800
cc

engines
In
this

type
of
carburettor
a

constant

flow
of
intake
air
is

maintained

by
the

automatically
adjusted

venturi

opening
this
is
accomplished

by
the
suction

piston

sliding
in
accordance
with

changes
in
the
volume
of
intake
air

Referring
to

Fig
D
5
the
suction
chamber
is
mounted
above

the
venturi
The
suction

piston
slides
vertically
within
the

chamber

and

changes
the
venturi

opening
area
The

piston
is

operated
by
a

difference
between
the

upper
vacuum

pressure

which
is

applied
through
the
suction

poct
and
the
atmospheric

pressure
which

is
introduced

through
the
air
hole
from
the
air

cleaner

The
amount

by
which
the
throttle
is

opened
causes
the

suction

piston
to
rise
or
fall
under
the
intluence
of
the

engine

suction
The

pozzle

opening
therefore

changes
and

provides
an

optimum
air
fuel
mixture
at
all

engine
speeds

The

cartridge
type
fuel
strainer
utilizes
a
fibre
strainer

element
which
should
be

replaced
every
20
000
km
12
000

miles
Removal
of
the
fuel
strainer
is
a

simple
operation
but
as

it
cannot
be
drained
the
strainer
should
not
be
removed
when
CARBURETIOR
Removal
and
Overhaul

FLOAT
LEVEL
Adjustment

SU
TWIN
CARBURmORS

Adjustments

SU
TWIN
CARBURmORS

Dismantling

SU
TWIN
CARBURETTORS

Inspection

STARTING
INTERLOCK
VALVE
OPENING

HYDRAULIC
DAMPER

the
tank
is

full
unless

absolutely
necessary

A

viscous

paper
type
air
cleaner
element
is
fitted
which

does
not

require
cleaning
and
should
be

repl
ced

every
40
000
km

24
000
miles
The
air

cleaner
fitted
on
the

single
carburettor

is
equipped
with
an

idling
compensator
to

prevent
the
mixture

from

becoming
too

rich
at

high
idling

temperatures
Additional

fresh
air
is
introduced
into
the
inlet
manifold

by
the
action
of

a
bimettalic

strip
located
in
the
air
cleaner
When
the

temperature

under
the
bonnet
is

high
the
bimetal
is

heated

by
the
hot
inlet

air
and
lifts
to
allow
the
valve
to

open
The

idling
compensator

valve

partially
opens
at

550
I310F
and
is

fully
open
at

650C

l490F
The
unit
cannot
be
dismantled
as

it
is

pre
sealed
and

correctly
adjusted
for
valve

timing
Fig
D
6
shows
the

layout

of

the
idling
compensator
piping

FUEL
TANK

Replacing

The
fuel
tank
can
be
removed
in
the
following
manner

Remove
the
rear
seat

and
back
rest

2
Take
out
the
board
behind
the
back
rest

3
Take
out
the

luggage
compartment
lining
board
and

disconnect
the
cable
to
the

petrol
gauge
unit

4
Disconnect
the
petrol
filler
tube
from
the
tank

5
Remove
the
tank
retaining
bolts
and
disconnect
the

rubber
fuel
outlet
and
return
hoses

Installation
is

a
reversal
of
the
removal

procedure
always

ensure
that
the
fuel
lines
arc
carefully
checked
for

signs
of

damage
before

replacing
the
tank

FUEL
PUMP

Testing

Pressure
and
capacity
tests
can
be
carried
out
with
the

pump
installed
in
the

following
manner

Static

pressure
test

Disconnect
the
fuel
line
at

the
carburettor
install
an

adaptor
tee

fitting
and
suitable

pressure
gauge
to
the
fuel
line

between
carburettor
and
fuel

pump
Start
the
engine
and
run
it

at

varying
speeds

The

reading
on

the
gauge
should
be
0
18
0
24

kg
sq

cm
2
6
34
Ib

sq
in
If
the

pressure
is
below
the

specified

figure
then
either
one

part
of
the

pump
has
worn

excessively

or

general
wear
has
occured
to

all
the

working
parts
The
faults

may
include
a

ruptured
diaphragm
worn
and

warped
valves

33