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 that fuel pump vacuum line
connections are tight and free of leaks.
1.
Operate engine at an idle for five minutes to ensure
that carburetor is full of fuel.
2.
Shut engine
off
and remove fuel inlet line from fuel
Pump.
71
Ignition of fuel can result in
severe personal injury or death.
Thoroughly clean up any spilled fuei
piece of fuel hose with clamps.
Record vacuum gauge reading.
3.
Connect a vacuum gauge tofuel pump inlet using a
4.
Start engine and allow to idle for five seconds.
5.
6.
7.
8.
9.
10.
Move throttle control to high idle position. Wait 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.
Remove fuel outlet line from fuel pump.
-1
Ignition
of
fuel can result in
severe personal iniurv or death.
Thoroughly clean up any spilled fuei
Connect a pressure gauge tofuel pump outlet using
a piece of fuel hose with clamps.
Start engineand allow to idle for five seconds. While
holding pressure gauge level with pump outlet
record pressure gauge reading.
Move throttle control to high idle position and allow
engine to run for 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.
Repair or replace the fuel pump
if
test readings are not
within the values specified
in
TABLE
1.
I
TABLE
1
PULSE PUMP TEST SPECIFICATIONS
Engine
Pump
Inlet
Pump
Outlet
Pressure
Speed
Vacuum
(Minimum) (Minimum)
Low
Idle
2.6
inches
1.7
psi
of
mercury
High
Idle
2.6
inches
1.7
psi
of
mercury
Fuel Pump Repair
This section applies only to Facet fuel pump. The Nikki
fuel pump is not repairable; replace unit
if
test readings
are not within the values specified in Table
1.
1.
Remove thevacuum and fuel lines. Inspect the lines
for wear, cracking or brittleness. Replace as
necessary.
2.
To insure correct alignment when reassembling,
scribe a line across the outer pump parts on each
end of the pump.
3.
Holding the pump carefully, remove the assembly
screws (Figure
5.)
4.
Carefully pull apart the pump sections and check for
worn
or
damaged parts. Install pump repair kit.
5.
Check and unclog
if
necessary the small diaphragm
air bleed hole located behind the pump diaphragm
in the pump base.
A
clogged diaphragm air bleed
ACAUTION
hole can cause diaphragm wear
and seal damage. Be sure air bleed hole
is
unclogged.
6.
Replace gaskets and reassemble pump. Reinstall
assembly screws, checking the scribe marks for
proper alignment. Reinstall fuel and vacuum lines
and clamps.
1
[-I
Improper fuel pump
parts
align-
ment
or
misconnected fuel lines
can result in leaking fuel, creafing a serious fire
hazard. Use extreme care when reassembling and
reinstalling fuel pump.
7-6
Redistribution or publication of this document,
by any means, is strictly prohibited.
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