JLG 601S Service Manual User Manual
Page 98
SECTION 3 - CHASSIS & TURNTABLE
3-58
– JLG Lift –
3120866
The linkage must not rub against the engine, brackets,
hoses, etc. The linkage must be free of friction and lost
motion or “slop”.
The following sketch indicates the proper linkage geome-
try for most installations.
Note that the angle between the carburetor arm and the
rod is 70 degrees with the engine at idle. This is highly
desirable! Note also that the Actuator arm travels equally
on either side of a 90 degree angle with the rod. This
angular arrangement will give the proper mechanical gain
for good stability and performance. It may be necessary to
rotate the carburetor arm relative to the butterfly to
achieve this. This can usually be done, and is usually
worth the effort! Below are some workable installations,
with good linkages. Remember, the Actuator can be
turned 180 degrees on its mounting to “reverse” the
spring-loaded direction. Also, the Actuator can be
mounted in any attitude.
The needed travel of the carburetor determines how far
out on the Actuator arm the rod is to be attached. In most
cases, the carburetor should be moved from closed to
above 10 degrees from full open as the Actuator is moved
min. to max. THEN ALTER THE LENGTH OF THE ROD
SLIGHTLY (PERHAPS 0.030"), SO THAT THE ACTUATOR
IS JUST OFF ITS INTERNAL STOP, AND IS PULLING THE
BUTTERFLY AGAINST ITS STOP. This insures that the car-
buretor can fully close to idle on load dumps, minimizing
overspeeds.
Examine the system for springs, such as carburetor return
springs. These should be removed. Some automotive car-
buretors (as opposed to industrial carburetors) contain
internal springs for accelerator pumps, etc. These may
make good governing difficult, or even impossible. For
this, and other reasons, industrial carburetors are much to
be preferred.
Move the linkage slowly through its travel, and look for
any binding or unexplained forces. Correct any before
going further.
Many “governing” problems are really caused by binding
of the butterfly and its shaft in the carburetor. This is
caused by loading due to vacuum under the butterfly and
atmospheric pressure above when the engine is running.
These forces cannot be felt when the engine is not run-
ning. Therefore, start the engine while carefully controlling
the speed by hand, and feel for binding or airload forces.
Needle bearings on the butterfly shaft are available on
many industrial carburetors to deal with this problem. Any
tendency on the butterfly stick must be corrected.