Generac Power Systems 941-2 Section CARBURETOR, General Information, Description, Carburetor

Section 3.4

CARBURETOR

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.

Page 3.4-1