Chevrolet 1977 light duty truck, Service Manual

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FUEL S U P P LY
FUEL FILTER
GEN ER A L D E S C R IP T IO N
All en g in e fuel filters are located in the carburetor
fuel inlet. These fuel filter elem ents are o f pleated paper.
Elements are placed in the inlet hole with the gasket
surface outw ard. A spring holds the elem ent outward,
sealing it by com pressing a gasket surface against the
inlet fitting.
O N-VEHICLE SERVICE
The ca rb u re to r inlet fuel filter should be replaced
every 15,000 miles or 12 months.
A fter assem bling any filter ele m ent in the car­
buretor, always start the engine and check for leaks in
the fuel line and fittings before installing the air cleaner.
Other Filters or Strainers
A woven plastic filter is located on the lower end o f
the fuel pickup pipe in the gas tank. This filter prevents
dirt from e n te rin g the fuel line and also stops water
unless the filter becomes completely subm erged in water.
This filter is self cleaning and norm ally required no
m ain ten an ce. Fuel stoppage at this point indicates that
the gas tan k contains an a b n o rm a l a m o u n t o f sedim ent
or water; the tank should therefore be removed and
thoroughly cleaned.
Fuel Filter R eplacem ent
Light Duty Emissions
A plugged fuel filter a n d / o r check valve will restrict
fuel flow.
1. Disconnect fuel line connection at fuel inlet
filter nut.
2. Remove fuel inlet filter nut from carburetor.
3. Remove filter and spring.
4. If removed, install check valve in fuel inlet filter.
CAUTION: The fu e l inlet check valve m ust be
installed in the filter to meet M otor Vehicle
S a fety Standards (M. V.S.S.) f o r roll-over. New
service replacement filte r include the check
valve.
5. Install fuel inlet filter spring, filter, and check
valve assembly in carburetor. Check valve end o f filter
faces toward fuel line.
N OTE: Ribs on closed end o f filter element
prevent filter from being installed incorrectly
unless forced.
6. Install new gasket on fuel inlet filter nut and
install nut in carburetor. Tighten nut to 18 pound feet.
CAUTION: Tightening beyond specified torque
can dam age gasket.
7. Install fuel line and tighten connection.
Heavy Duty Emissions
A plugged fuel filter will shut off fuel flow into
carburetor.
1. Disconnect fuel line-connection at inlet fuel
filter nut.
2. Remove inlet fuel filter nut from carburetor.
3. Remove filter element and spring.
4. Install elem ent spring an d filter elem ent in
carburetor.
5. Install new gasket on inlet fitting nut and install
nut in c arburetor and tighten securely.
6. Install fuel line and tighten connector.
FUEL
G E N ER A L D E S C R IP T IO N
T he fuel p u m p (Figs. 6C-59 through 61)) is a
d i a p h r a g m type p u m p and is actuated by the rocker arm
through a link an d a push rod.
Som e vehicles have a fuel pu m p which has a
m etering outlet for a vap o r retu rn system. A ny vapor
which form s is returned to the fuel tank along with hot
fuel th ro u g h a separate line. This greatly reduces any
possibility o f v a p o r lock by keeping cool fuel from the
tank constantly circulating thro u g h the fuel pump.
O N -VEH IC LE SERVICE
Inspection and Test
If the fuel system is suspected o f delivering an
PUMP
im p ro p e r a m o u n t o f fuel to the carburetor, it should be
inspected and tested in the vehicle, as follows:
Inspection of Fuel System
1. M ake certain that there is gasoline in the tank.
2. W ith the engine running, inspect for leaks at all
gasoline feed hose connections from fuel tank to
carburetor. Tighten any loose connections. Inspect all
hoses for flattening or kinks which would restrict the flow
o f fuel. A ir leaks or restrictions on suction side o f
mechanical fuel p u m p will seriously affect p u m p output.
3. Inspect for leaks at fuel p u m p d ia p h ra g m
flange.
4. Disconnect feed pipe n e a r carburetor. G ro u n d
d istributor te rm inal o f coil with ju m p e r wire so that
engine can be cranked without firing. Place suitable