Service Manual
PULSATING-DIAPHRAGM FUEL PUMP
Pulsating-diaphragm fuel pumps,
or
pulse pumps, rely
on changes in crankcase vacuum to create a pulsating
movement of the pump diaphragm.
As
the engine's
pistons move outward, a vacuum is created. This
vacuum is transmitted to the pump diaphragm causing
it
to pull back and suck fuel into the pump.
As
the engine's
pistons move inward, crankcase vacuum is reduced
and the diaphragm return spring pushes the pump
diaphragm forward, forcing fuel through the pump
outlet.
serious
personal injury
or
death.
Spilled fuel can
ignite and
cause
Thoroughly
clean-up
any
spilled
fuel.
7.
Remove fuel outlet line from fuel pump.
8.
Connect a pressure gauge to fuel pump outlet using
a piece of fuel hose with clamps.
9.
Start
engine and allow to idle for at least five
seconds. While holding pressure gauge level with
pump outlet record pressure gauge reading.
10.
Move throttle control
to
high idle position and allow
engine to run for at least five seconds. While holding
pressure gauge level with pump outlet record
pressure gauge reading.
Fuel
Pump
Test
Procedure
Before testing make certain the fuel pump vacuum and
fuel
line connections are tight and
free
of
leaks.
1.
2.
3.
4.
5.
6.
Operate engine at an idle
for
five minutes to ensure
that
carburetor
is
full
of fuel.
Shut engine
off
and remove fuel inlet line from fuel
pump.
Connect a vacuum gauge to fuel pump inlet using a
piece of fuel hose with clamps.
Start
engine and allow to idle for
at
least five
seconds. Record vacuum gauge reading.
Move throttle control to high idle position. Wait at
least five seconds and record vacuum gauge
reading.
Shut engine
off
and remove vacuum gauge hose
from fuel pump inlet. Connect fuel inlet line to fuel
pump-
11.
Shut engine
off
and remove pressure gauge hose
from fuel pump outlet Connect fuel outlet line
to
fuel
pump.
Replace the fuel pump
if
test readings are not within the
values
specified
in
TABLE
1.
TABLE
1
PULSE PUMP TEST SPECIFICATIONS
ENGINE
PUMP
INLET
PUMPOUTLET
SPEED VACUUM
PRESSURE
(Minimum)
(Minimum)
Low Idle
2.6
inches
1.7
psi
of mercury
High Idle
2.6
inches
1.7
psi
of mercury
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