Fuel System Operation and Tests
ADJUST VARIABLE SPEED (DROOP) ON
DB2 AND DB4 INJECTION PUMPS
An external speed droop adjusting cap (A) at the rear of
the injection pump housing provides precise control of
governor sensitivity by decreasing or increasing the
effective length (and thereby the rate) of the governor
control spring. Fine adjustments can be made while the
engine is operating.
1. Start engine and run at rated speed with 50% load
applied until it reaches normal operating temperature.
NOTE: If serious surging occurs during the warm-up
period, turn the speed droop adjusting cap
clockwise until surging stops.
2. When engine has warmed to normal operating
temperature, position throttle lever (D or E) to attain full
load rated speed (e.g., 1500, 1800 RPM) and apply
100% (full) load.
Adjust the throttle if necessary to obtain satisfactory full
NOTE: Whenever speed droop adjustments are made,
throttle position adjustments will also be
3. Remove load and check for specified no-load speed or
If incorrect, adjust speed droop adjusting cap slightly
(clockwise for increased droop or counterclockwise for
If surging exists upon removing the load, turn the
adjusting cap clockwise to eliminate.
4. Recheck full load and no-load performance and
readjust as necessary.
A--Speed Droop Adjusting Cap
B--Fast Idle Screw
C--Slow Idle Screw
D--Early Throttle Lever