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.
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.
lgnition of fuel can result in
severe personal injury or death.
Thoroughly clean up any spilled 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.
Ignition fuel can result in
severe personal injury or death.
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.
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 SPEClFICATlONS
ENGINE PUMP INLET PUMP OUTLET
SPEED VACUUM PRESSURE
(Minimum) (Minimum)
Low Idle 2.6 inches 1.7 psi
of mercury
High ldle
2.6 inches 1.7 psi
of mercury
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