Service Manual
IMPULSE FUEL .PUMP
The engine may be equipped with an impulse type
fuel pump that uses crankcase pressure (vacuum)
pulses to operate a spring loaded diaphragm inside
the pump to pump the fuel through
two
check
valves. Engine crankcase vacuum is connected
through a hose to the back of the pump. The fuel
flow direction is marked on the cover of the pump.
Use
adequate ventilation when working on the fuel
system. Prevent ignition sources in the areas shar-
ing ventilation.
If
the fuel pump leaks, replace it. This fuel pump is
not intended to be rebuilt for
a
fuel leak problem.
WARNING
ignition
of
fuel can result in severe
personal injury or death.
Do not smoke
or
allow
any spark, pilot light, or arcing switch
or
equip-
ment near the fuel system or in areas with
shared ventilation.
Inspection/Service
If
a problem with fuel delivery to the engine is
sus-
pected, check the following items before inspecting
the fuel pump.
1.
Make sure the fuel shutoff valve is open.
3.
Make sure the fuel hoses are not kinked or
pinched, causing a fuel restriction. Dips and ex-
cessively long runs of fuel line in a hot area can
cause vapor locking.
2.
Check the fuel filter and replace
it
if
required.
4.
Check the fuel tank cap for a restricted vent.
5.
Check the oil level to make sure
it
is at the full
mark.
6.
Inspect the crankcase, especially at the gas-
kets, for visible oil leaks, indicating crankcase
air leakage that can cause reduced fuel pump
performance.
Also
check the seal
on
the oil
fill
tube.
7.
If
the gasoline has been stored for an extended
time, drain and properly dispose of the old gas-
oline. Refill the fuel tank with fresh unleaded
regular gasoline.
If
fuel delivery problems still occur, perform the fol-
lowing performance checks based on the symptom.
Engine
Will
Not
Start:
Crank the engine, then im-
mediately remove and inspect the spark plug.
If
the
plug
is
wet and
it
has a strong gasoline odor,
check for:
An ungrounded ignition ground wire
A
defective throttle plate or low oil pressure
switch or other equipment switch for ignition
grounding
A fouled spark plug
An improperly adjusted carburetor choke
If
the
plug Is
dry,
ground the spark plug lead
so
that'
ignition sparks can not ignite the gasoline.
Remove the fuel line from the carburetor and splice
in a
fuel
line of approximately eight inches in length.
Place the end of the fuel line in
a
container to collect
the gasoline Crank the engine with the electric
starter
or
the recoil starter for
20
seconds. There
should be fuel flow into the container.
If
there is no
fuel flow from the pump, replace the fuel pump
as
instructed in this section.
Engine Runs But
Will
Not Operate At High Load:
If
the engine starves for fuel at high load, connect a
gravity feed fuel supply directly to the carburetor.
Plug the fuel line from the fuel pump during this test.
If
the gravity feed fuel supply eliminates fuel starva-
tion, replace the fuel pump
as
instructed in this
sec-
tion.
If
the fuel starvation continues, the fuel pump is
not the cause.
9-3