Section 4.1

INTRODUCTION TO FUEL SYSTEM

GASEOUS CARBURETION

Gas at positive pressure is delivered from the fuel lockoff solenoid to the inlet of the regulator (about 11- 14 inches of water).

As the engine piston moves downward on its intake stroke, air is drawn into the area above the piston through the carburetor venturi. A negative pressure is created at the venturi which is proportional to the amount of air that is flowing.

The negative pressure at the carburetor venturi acts on the regulator diaphragm to pull the diaphragm toward the source of low pressure. A lever, attached to the diaphragm, opens a metering valve which allows gas to enter and flow through the carburetor.

The greater the air flow through the carburetor ven- turi, the lower the pressure at the venturi throat. The lower the pressure at the venturi throat, the greater the movement of the diaphragm and the more the metering valve opens.

Figure 2. Gas Carburetion Diagram

The following requirements of the secondary regulator must be emphasized:

It must be sensitive to pressure changes in the car- buretor venturi throughout the entire operating range.

It must positively stop the flow of gas when the engine is not running.

The slightest air flow through the carburetor venturi must move the regulator valve off its seat and per- mit gas flow.

LEAKAGE TESTING

Whenever any lines, fittings or other components of the fuel system have been removed and replaced, the system should be carefully checked for leaks before it is placed into service.

To check for leakage, start the engine and let it run. Then use a soap and water solution or an approved commercial leak detector solution to determine if any leakage exists. No leakage is permitted.

DANGER! DO NOT USE FLAME TO CHECK

!FOR LEAKAGE. GASEOUS FUEL LINES BETWEEN THE TANK AND SECONDARY REGULATOR ARE UNDER A POSITIVE PRES- SURE (ABOUT 11 INCHES OF WATER COL- UMN). HOWEVER, GAS PRESSURE AT THE OUTLET SIDE OF THE SECONDARY REGU- LATOR IS A NEGATIVE PRESSURE (ABOUT 1 INCH WATER COLUMN). THIS NEGATIVE PRESSURE CAN DRAW FLAME INSIDE A LINE OR FITTING AND CAUSE AN EXPLO- SION.

IMPORTANT! APPLY PIPE SEALANT TO

!THREADS OF ALL FITTINGS TO REDUCE THE POSSIBILITY OF LEAKAGE.

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Generac Power Systems 941-2, 940-2 service manual Introduction to Fuel System Gaseous Carburetion, Leakage Testing

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