Generac Power Systems 941-2 Service Manual page 63

GENERAL INFORMATION
Proper engine performance depends on the carbure-
tion system. The use of clean, fresh gasoline and a
well-maintained air cleaner are extremely important to
proper operation, as well as engine reliability and
power.
Most causes of carburetion problems are related to
the use of stale, gummy fuel and the ingestion of dirt.
Before servicing the carburetor, be sure to check for
evidence of these conditions. Gasoline that is left in
the fuel lines for long periods can form gum or varnish
deposits that will adversely affect carburetor opera-
tion.
NOTE: A commercial fuel stabilizer (such as STA-
BIL®) will minimize the formation of um deposits
during storage. Add the stabilizer- to the gasoline
In the fuel tank or In the storage container. Follow
the ratio recommended on the stabilizer contain-
er. Run the engine for about 10 minutes after
adding stabilizer, to allow It to enter the carbure-
tor. "STABIL®" Is a brand name fuel stabilizer that
can be purchased In most automotive repair facili-
ties or in lawn and garden centers.
DESCRIPTION
The carburetor used on GV-220 engines is a float type
with fixed main jet. Carburetor throttle position and
engine speed are controlled by an electric stepper
motor. The stepper motor moves the throttle in
response to signals received from the A6060 circuit
board. The circuit board senses load voltage, establish-
es the correct engine speed to obtain correct voltage
and delivers an output signal to the stepper motor. The
stepper motor adjusts the engine throttle to change
engine speed and establish correct output voltage.
Figure 1. Carburetor
CARBURETOR OPERATION
FLOAT OPERATION:
A hollow plastic float maintains fuel level in the float
bowl. As fuel is used, the float moves downward to
move an inlet needle valve off its seat.
When the needle valve moves off its seat, fuel can
flow into the bowl. As the fuel level rises, the float
moves upward to force the needle valve against its
seat and stop the flow into the bowl.
Figure 2. Carburetor Sectional View
CHOKE POSITION:
The choke valve is closed to restrict the flow of air
into the engine. As the engine cranks, air pressure in
the cylinder is reduced. Since the air intake passage
is partially blocked by the choke valve, fuel is drawn
from the main nozzle and from the idle discharge port.
This creates the very rich fuel mixture required for
starting a cold engine.
IDLE OPERATION:
The throttle valve is nearly closed to shut off the fuel
supply from all ports except the primary idle fuel dis-
charge port. Engine suction then draws fuel only from
that port.
HIGH SPEED OPERATION:
The throttle valve is wide open. This allows a large
volume of air to pass through the carburetor at a high
velocity. The high velocity air flow past the carburetor
venturi results in a drop in air pressure at the venturi
throat. This reduced air pressure draws fuel through
the main nozzle that opens into the venturi which then
mixes with the air in the air passage.
Section 3.4
CARBURETOR
Page 3.4-1