Buick LeSabre 1965 Service Manual page 105

ENGINE FUEL A N D EXHAUST SYSTEMS
FUEL PUMP 3 - 2 9
As the rotating eccentric permits
the rocker arm to swing upward,
the arm releases the fuel link;
it cannot move the link downward.
The compressed diaphragm spring
then e x e r t s pressure on the
diaphragm and the fuel in the
chamber below diaphragm. This
pressure closes the inlet valve
and forces fuel out through the
outlet valve to the carburetor.
Since the fuel diaphragm is moved
downward only by the diaphragm
spring, the pump delivers fuel to
the carburetor only when the
pressure in the outlet line is less
than the pressure maintained by
the diaphragm spring. This con-
dition arises when the carburetor
float needle valve is not seated
and the fuel passage from the
pump into the carburetor float
chamber is open. When the nee-
dle valve is closed and held in
place by the pressure of the fuel
on the float, the pump builds up
pressure in fuel chamber until it
overcomes the pressure of the
diaphragm spring. This pressure
results in almost complete stop-
page of diaphragm movement until
more fuel is needed.
The air dome with diaphragm in
the bottom of fuel pump provides
a pocket in which fuel under pres-
sure can compress a certain vol-
ume of air. When the pressure is
relieved (pump on suction stroke)
the pocket of compressed air
pushes the fuel on to its destina-
tion. The air dome minimizes
flow variations experienced with
two-cycle pump stroke and in-
creases the pump output.
3 - 1 2 FUEL PUMP
INSPECTION AND
TEST
NOTE: For test procedures on
the 300 engine fuel pump, see
p a r a g r a p h 3-12 of the Buick
Special Chassis Service Manual.
If the fuel system is suspected
of delivering an improper amount
of fuel to the carburetor, it should
be inspected and tested on the
engine, as follows:
a. Inspection of Fuel System
1. Make certain that there is
gasoline in the tank.
2. Clean the g a s o l i n e filter
(par. 3-7).
3. With engine running, inspect
for leaks at all gasoline feed hose
connections at gasoline t
a
nk, fuel
pump, and carburetor. Tighten
any loose connections. Inspect all
hoses for flattening or kinks
which would restrict the flow of
fuel. Air leaks or restrictions on
suction side of fuel pump will
seriously affect pump output.
4. Inspect for leaks at fuel pump
diaphragm flange. To correct,
tighten cover screws alternately
and securely.
5. Disconnect feed pipe at car-
buretor. Ground distributor ter-
minal of coil with jumper wire
so that engine can be cranked
without firing. Place suitable con-
tainer at end of pipe and crank
engine a few revolutions. If no
gasoline, or only a little flows
from pipe, the feed line is clogged
or fuel pump is inoperative. Be-
fore condemning the fuel pump,
disconnect feed lines at pump and
blow through them with air hose
to make sure that they are clear.
6. If gasoline flows in good vol-
ume from pipe at carburetor it
may be assumed that the fuel
pump and feed line are okay;
however, it is advisable to make
the following "static pressure''
test to make certain that fuel
pump is operating within specified
pressure limits.
b. Fuel Pump Pressure Test
1. Disconnect gasoline pipe at
carburetor and connect a suitable
pressure gauge to pipe at car-
buretor height.
2. Start engine and check pres-
sure with engine running at slow
idle speed. If pressure is not
between 4-3/4 and 6-1/2 pounds,
pump should be removed for re-
pairs (par. 3-13).
NOTE: If pressure gauge is at
pump height instead of at car-
buretor height, the p r e s s u r e
should be 1/2 pound higher.
3 - 1 3 FUEL PUMP REPAIRS
There are two service kits avail-
able: 1. The diaphragm kit con-
sisting of diaphragm, valves, and
oil seal. This kit is used for
overhauling low mileage pumps.
2. The repair kit consisting of
all moving and wearing parts ex-
cept the rocker arm. This kit is
used for overhauling high mileage
pumps. However, if a casting is
damaged or the rocker arm is
badly worn, it is advisable to
replace the pump rather than at-
tempt repairing it.
After removal of pump from en-
gine and before disassembly is
started, plug all openings and
thoroughly wash exterior of pump
with cleaning solvent to remove
all dirt and grease.
a. Disassembly of Fuel Pump
NOTE: For instructions on the
disassembly and assembly of the
fuel pump on the 300 engine, see
paragraph 3-13 of the Buick
Special Chassis Service Manual.
1. Mark edges of fuel cover and
pump body with file so that cover
may be reinstalled in its original
position on body. See Figure 3-23.
2. Remove all fuel cover screws
and separate cover from pump
body. If cover sticks to body, rap
with soft mallet - do not pry be-
tween parts with a screwdriver.
3. Remove pulsator cover and di-
aphragm from fuel cover. Scrape
out burrs produced by staking