Bumper Spring Adjustment
Check to be sure that external pump control linkage travels 0.125 to 0.375 in. (3 to 9 mm)
beyond pump control lever with pin connecting linkage to pump lever removed, and
accelerator pedal or governor control lever is on its high idle stop screw.
Bumper spring adjustment screw for idle surge control is preset to protrude 0.450 in. (11.4 mm) from locknut to slot-
ted end of adjustment screw. This adjustment is to be changed only if it is necessary to eliminate surging. If neces-
sary, adjust as follows:
a. Remove bumper screw cap.
b. Loosen bumper spring adjustment screw locknut and turn screw in to just contact at speed at which surge
Tighten locknut and recheck high idle speed. If high idle has increased to more than 20 RPM above
maximum idle speed stamped on vehicle serial number plate, back-out bumper spring adjustment screw
locknut and reset high idle to low side of specified RPM range.
d. Readjust bumper spring to eliminate surge.
Engine RPM must not exceed that specified, as it will definitely affect rated load
operations. Low idle speed is automatically adjusted when external pump control linkage
is adjusted correctly.
Low Idle Speed Adjustment
1. Check and adjust low idle speed as follows:
a. Check engine low idle speed (650 RPM ± 25 RPM).
b. If out of specified speed, remove capnut from low idle adjustment screw (located above bumper spring
Loosen low idle adjustment screw locknut and adjust to specified low idle. Tighten locknut and install cap