Onan CCK Service Manual

REGULATOR
The IMPCO pressure regulator is a two-stage
regulator (LP Gas Converter) with a hand primer.
Figure 28. it should be trouble and maintenance free
for extended periods of operation. Repair kits are
available for a complete overhaul if a malfunction
occurs. The kit includes detailed and illustrated
installation instructions. The secondary regulator
lever assembly is subject to wear under heavy duty
operation and may require replacement during an
overhaul. The low pressure spring (blue) forvacuum
control gives a negative 1-1/2-inch water column
measurement on a manometer. The two vapor outlet
ports and the LPG inlet have 1/2-inch pipethread. The
balance line connection is 1/8-inch pipethread.
FIGURE 28. GAS REGULATOR
GAS CARBURETOR
The IMPCO carburetor or mixer employs a unique,
moving venturi {air valve, metering valve and venturi
combined) to measure airflow, to meter gas flow, and
to mix the intake air and gas, Figure 29. The throttle
controls engine speed and power in the same way as
the carburetors on other gas or gasoline engines. An
idle jet, a mam jet (power mixture adjustment) and a
throttle stop screw provide carburetor adjustments
for maximum engine power and efficiency with low
exhaust emissions.
CARBURETOR OPERATION
in operation, the moving venturi/air valve or air valve
assembly opens in direct proportion to the breathing
requirements of the engine to give optimum mixtures
and good air/fuel distribution, Figure 30.
FIGURE 29. GAS CARBURETOR
The air valve assembly operates in an up-and-down,
piston-like motion inside the cylindrical cavity of the
throttle body assembly. When the engine is stopped,
the air valve assembly is held in a closed position by a
metering spring. Figure 30A.The gas passage in the
throttle body is completely closed off by means of a
synthetic rubber seat on the metering valve. When the
engine is started, the air valve assembly moves
downward off the gas passage inlet, allowing entry of
gas into the venturi throat where it mixes with high-
velocity intake air. Figure 30B. The higher the load
demand, the greater the air and gas opening up to
maximum throttle.
Carburetor vacuum provides a sufficiently strong
metering signal (or metering force) to the fuel
regulator. The better the signal, the less important
precise pressure regulation of the fuel becomes.
Under heavy pulsing conditions with two-cylinder
engines, oscillations of the air valve are reduced by a
breather hole with a check valve in the plate that
supports the air valve and spring. The check valve
vents air allowing the air valve movement and relieves
any pressure surges caused by backfire, without
closing the air valve.
A constant depression spring positioned between the
check valve and the air valve assembly provides
constant tension against the air valve to keep the
vacuum curve flat. This spring limits the vacuum
signal transmitted from the intake manifold, holding it
between 0.5-and 1.5-inches of mercury. The constant
tension on the air valve assembly amplifies the signal
at idle and limits it at full throttle. The air valve
provides good breathing at top speed, eliminates flat
spots at low speeds, and prevents lag in the pulse
signal to the regulator. Therefore, throttle response is
good with fast acceleration.
33

Onan CCK Specifications

General

Cylinders	2
Ignition System	Battery ignition
Fuel Type	Gasoline
Cooling System	Air-cooled
Fuel System	Carburetor
Starter	Electric
Governor	Mechanical
Max RPM	1800 RPM
Engine Type	4-cycle
Bore and Stroke	3.25 x 3.625 inches (82.55 x 92.08 mm)