REGULATOR AS 3770008 - Caterpillar

The signal air pressure range should be 35 kPa (5 psi) below the pressure at which the governor reaches low idle and 35 kPa (5 psi) above the pressure at which the governor reaches high idle. For example, if the governor's pneumatic control is factory set to reach low idle at 34.5 kPa (5 psi), the signal pressure at the minimum throttle setting should not exceed 0 kPa (0 psi). If the governor's pneumatic control is factory set to reach high idle at 365 kPa (52.9 psi), the signal pressure at the maximum throttle setting should be 400 kPa (57.9 psi) or 35 kPa (5 psi) more.
Pneumatic speed setting control.When the pressure signal from the remote throttle has been found to be correct, the pneumatic speed control on the governor can be adjusted according to the 3161 Governor Service Manual (SENR3028).
To confirm that the signal air pressure is moving the governor to high and to low idle, the governor face plate can be removed. You can now see if the speed setting shaft lever makes contact with both the low speed and high speed stop screws.
If the speed setting shaft lever does not contact the low speed stop screw (no signal air pressure to the pneumatic control), the engine speed will not drop when the low idle screw is backed out. Before doing the governor pneumatic speed control adjustment procedure in the service manual, turn the speed level adjustment screw (on governor pneumatic speed control) until the speed setting shaft lever contacts the low idle screw.