Generac Power Systems GTH760, Service Manual

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3-4
SeCTIoN 3: CArbureTIoN ANd Fuel SYSTeM
The pump consists of (see Figure 3-10):
1. Lower Spring assembly
2. Lower Diaphragm
3. Check Valve Assembly
4. Upper Diagram
5. Upper vent Assembly
6. Mounting Hardware x 2
As a vacuum is built up in the crankcase the Lower Dia-
phragm will be pulled down against the Spring Return. When
the Lower Diaphragm is pulled inward fuel will flow through
Check-Valve 2. As pressure is built in the crankcase the Spring
Return will push the Lower diaphragm up. When the Lower
diaphragm is pushed up fuel will flow through Check-Valve 1
and out the fuel port.
lP (lIquId) - Fuel SYSTeM
*
Proper service and repair is important to the safe
and reliable operation of all gaseous fueled engines.
Any servicing or testing of a gaseous fueled engine
must only be performed by qualified personnel.
Always follow applicable installation and service
procedures. An example of these requirements is
found in NFPA-52 for natural gas. These are uS
Federal standards. worldwide standards vary. local,
city, and state requirements may also have certain
requirements that must be observed.
LP (Liquefied Petroleum Gas) is a gaseous fuel and when
stored under pressure, becomes a liquid. Although a vapor
forms at the top of the tank, this particular system uses a liquid
withdrawal method, drawing from the bottom of the tank.
This is accomplished with a special valve that is installed on a
normal propane cylinder with a tube that is attached to the
valve and extends to the bottom of the storage tank. Because
of pressure in the tank, liquid propane is forced through the
tube when the valve is opened.
The Generac LP system starts with a pressure relief valve to
prevent excessive pressure from building in the system during
shutdown. This is followed by a 12 volt (normally closed) elec-
tric solenoid, which prevents the flow of fuel when the ignition
key is off. When the ignition key is turned on, the solenoid
opens and allows liquid LP to flow to the regulator.
The liquid fuel vaporizer regulator converts liquid propane to
a vapor. The vaporizer uses spent engine cooling to provide
heat to aid in the evaporation process. The regulator controls
the vapor supply to an amount required by the engine. The
engine’s intake vacuum draws LP into the carburetor on an
on-demand need. When the engine is off, the LP no longer
flows from the regulator to the engine (see Figure 3-32).
Trouble SHooTING
*
CAuTIoN! Gaseous fuels are highly explosive; do not
use flame or heat to test the fuel system for leaks.
lP gas is heavier than air and tends to settle in low
areas; even the slightest spark can ignite these gases
and cause an explosion.
Note: Don’t assume that the fuel system is the problem.
Verify that the engine has spark and enough compres-
sion to start the engine before proceeding with the
following steps.
SPRING
RETURN
1 2 3 4 5 6
LOWER
DIAPHRAGM
UPPER
DIAPHRAGM
VENT: UPPER
VENT ASSEMBLY
FUEL
CHECK-
VALVE 1
FUEL
CHECK-
VALVE 2
HARDWARE
Figure 3-10. Fuel Pump Assembly