5.2
Section 5
Fuel System and Governor
Fuel Pump
General
Most engines are equipped with an optional
mechanically operated fuel pump. On applications
using a gravity feed fuel system, the fuel pump
mounting pad is covered with a metal plate.
The fuel pump body is constructed of nylon. The
nylon body insulates the fuel from the engine
crankcase. This prevents the fuel from vaporizing
inside the pump.
Operation
The mechanical pump is operated by a lever which
rides on the engine camshaft. The lever transmits a
pumping action to the diaphragm inside the pump
body. On the downward stroke of the diaphragm, fuel
is drawn in through the inlet check valve. On the
upward stroke of the diaphragm, fuel is forced out
through the outlet check valve. See Figure 5-2.
Figure 5-2. Cutaway - Typical Fuel Pump.
Diaphragm
Inlet Check Valve
Fuel Pump
Lever
Camshaft
Outlet Check Valve
Test Conclusion
1. Check for 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.
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.
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 for
clogged fuel tank vent, fuel pick-up screen, in-line
filter, shut-off valve, and fuel lines.
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
clogged fuel line. If the fuel line is unobstructed,
the fuel pump is faulty and must be replaced.
2. Check for fuel in the combustion chamber.
a. Disconnect and ground spark plug lead.
b. Close the choke on the carburetor.
c. Crank the engine several times.
d. Remove the 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.
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.
Troubleshooting - Fuel System Related Causes
To Next Page
Loading...
Need help?
General