JLG 450AJ ANSI Service Manual - Manual (Page 72)

SECTION 2 - PROCEDURES
2-54 – JLG Lift – 3120749
d. By carefully varying engine speed, you should
be able to cause the Governor arm to pause
momentarily near the middle of its travel. This
engine speed is the speed for which the Gover-
nor is adjusted. If grossly incorrect, reset High
Engine Pot.
e. With the engine running at low speed, move the
Governor arm throughout its stroke by hand.
You should feel a constant smooth force in the
on direction. No binding or rubbing should be
felt within the Governor.
If steps 1a. thru 1e. can be accomplished as described,
the Governor is probably OK. It recognizes underspeed,
overspeed, onspeed and is not binding internally.
If the above steps cannot be accomplished satisfactorily,
there is probably an actual Governor malfunction.
2. Installation and adjustment problems.
Governor is unable to move fuel system freely (not
enough Actuator force available). If Governor doesn’t
move fuel system to on far enough to provide sufficient
fuel but Governor arm moves far enough when discon-
nected look for:
a. Linkage binding or misadjusted.
b. Low voltage at Governor during operation.
*Measure the voltage as discussed previously
and observe voltage during operation. If Gover-
nor fails to move full on and voltage dips over 1
volt, check for undersize wire (should be #16
minimum).
c. Excessive forces at Governor during running,
particularly on carburetor engines.
*Carburetor butterfly valves are loaded by
engine vacuum during running, which can add
considerable force not present when engine
isn’t running.
*Springs in the system; carburetor return
springs, acceleration pump springs, etc., are not
usually needed and can cause governing prob-
lems.
Governor is unstable at light-load or no-load. See Linkage
for carbureted engines.c.
Governor experiences sudden, momentary spikes toward
max. at random intervals, then recovers.
a. Look for loose wiring or momentary shorts in
wiring.
b. Noise or occasionally missing speed signal.
Speed seems to slowly wander (5-15 second periods)
around at speed, particularly at higher loads. See item 2a.
3 concerning excessive loads on Governor.
3. Governor not tuned or adjusted for engine/applica-
tion.
The basic adjustment to set sensitivity/stability is the Gain
pot. A good starting point for many engines is full CCW,
then CW 1/3 turn. (See Governor adjustment section). To
increase stability, turn CCW. If satisfactory governing can-
not be achieved with this one adjustment, the factory
adjustment may be needed. Normal starting point for this
adjustment is fully CCW, then CW 1/4 turn. (Before chang-
ing this pot, mark the original position).
NOTE: If problems occurs with the Governor overshooting
when a large load is released from the engine, such
as driving up a hill and stopping. There is usually
one of two things:
1. Gain adjustment is to far CCW.
2. Mechanical preload between the carburetor and
actuator is to large, this should be no greater than 1/
2 to 1 ball dia.