Kohler LH630-775 Service Manual page 29

Section 5
Fuel System and Governor
Fuel Filter
Most engines are equipped with an in-line fuel filter.
Periodically inspect the filter and replace with a
genuine Kohler filter every 200 operating hours.
1. Check the following:
a. Make sure the fuel tank contains clean, fresh,
proper fuel.
b. Make sure the vent in fuel tank cap is open.
c. Make sure the fuel valve is open.
d. Make sure vacuum and fuel lines to fuel
pump are secured and in good condition.
2. Check for fuel in the combustion chamber.
a. Disconnect and ground the spark plug leads.
b. Close the choke on the carburetor.
c. Crank the engine several revolutions.
d. Remove a spark plug and check for fuel at the
tip.
3. Check for fuel flow from the tank to the fuel
pump.
a. Remove the fuel line from the inlet fitting of
fuel pump.
b. Hold the line below the bottom of the tank.
Open the shut-off valve (if so equipped) and
observe flow.
4. Check the operation of fuel pump.
a. Remove the fuel line from the inlet fitting of
carburetor.
b. Crank the engine several times and observe
flow.
Fuel Pump
General
These engines are equipped with either a mechanical,
or pulse style fuel pump. See Figure 5-1.
5.2
Troubleshooting – Fuel System Related Causes
Test
Fuel System Tests
When the engine starts hard, or turns over but will not
start, it is possible that the problem is in the fuel
system. To find out if the fuel system is causing the
problem, perform the following tests.
Conclusion
2. If there is fuel at the tip of the spark plug, fuel is
reaching the combustion chamber.
If there is no fuel at the tip of the spark plug,
check for fuel flow from the fuel tank (Test 3).
3. If fuel does flow from the line, check for faulty
fuel pump (Test 4).
If fuel does not flow from the line, check the fuel
tank vent, fuel pickup screen, in-line filter, shut-
off valve, and fuel line. Correct any observed
problem and reconnect the line.
4. If fuel does flow from the line, check for faulty
carburetor. (Refer to the "Carburetor" portions of
this section.)
If fuel does not flow from the line, check for a
clogged fuel line. If the fuel line is unobstructed,
check for overfilled crankcase and/or oil in pulse
line. If none of the checks reveal the cause of the
problem, replace the pump.
Operation
Pulse Fuel Pump
Operation and pumping action is created by
alternating positive and negative pressures within the
crankcase. This pressure is transmitted to the pulse
pump through a rubber hose connected between the
pump and the crankcase. The pumping action causes
the diaphragm on the inside of the pump to pull fuel
in on its own downward stroke and to push it into the
carburetor on its upward stroke. Two check valves
prevent fuel from going backward through the pump.