ELEMENT AS-BREATHER 4211888 - Caterpillar

Check the fuel pressure before the gas pressure regulator and after the gas pressure regulator. Table 1 lists the fuel pressure that is required for the gas pressure regulator.
Table 1
Requirements for Fuel Pressure To the Gas Pressure Regulator    
Fuel System     Pressure    
Low pressure gas
Naturally Aspirated    
10.3 to 34 2 kPa (1.50 to 5 0.25 psi)    
High pressure gas    
172 to 207 7 kPa (25 to 30 1 psi)    Pressure of the Fuel Supply To the Carburetor
The gas pressure regulator maintains a pressure differential between the air and the fuel that is supplied to the carburetor. After setting, the gas pressure regulator will maintain the pressure differential in response to changes in the air pressure.Use a water manometer for measuring the pressure differential. Obtain the measurement when the engine is operating at high idle rpm. After a load is applied, the fuel pressure will usually decrease by approximately 0.1 to 0.25 kPa (0.50 to 1 inches of H2O). If the performance of the gas pressure regulator is erratic, the gas pressure regulator may require service.Natural Gas
Set the pressure of the fuel supply to a maximum of 1 to 1.2 kPa (4 to 4.5 inches of H2O) HIGHER than the ambient air pressure.Propane
Set the pressure of the fuel supply to -0.37 -0.06 kPa (-1.5 0.250 inches of H2O) LOWER than the ambient air pressure.Note: If the engine is equipped with a vaporizer/regulator for liquid propane fuel supply, the vaporizer/regulator will regulate the fuel supply pressure at the correct level. No adjustment is required.