The latest service manual that I located online for the Onan KY 4000KW generator set was a 2006 manual that covers gen sets through Spec J. Of course, a lot still fully applies to later sets, so I had downloaded a copy---and the instructions for choke adjustment may still be valid. I hate to string out this post, but the easiest way for me to pass on the information is to just copy and paste it, so below is what it says.
(Apologies for the long post), Mike
The genset has an automatic choke assembly that
consists of a bimetal choke coil, coil housing, heater
tube (from the exhaust tube), and choke linkage.
The choke linkage connects to the choke shaft lever
on the carburetor.
When the engine is cold, the choke coil position
causes the linkage to hold the choke nearly closed.
When the engine starts, hot air from the exhaust
manifold enters the coil housing. The choke coil expands
pulling the linkage to partially open the
choke. As the engine warms up, the coil continues
to expand and gradually opens the choke and holds
it open while the engine is operating.
If the engine starts but runs rough and exhausts
black smoke after a minute or two of operation, the
choke setting is too rich. If the engine starts but sputters
or stops before it warms up, the choke setting is
too lean.
Choke Adjustment: Check the choke linkage to
make sure it is not bent or rubbing. Rotate the choke
lever on the carburetor. The choke shaft should
move freely and it should return to its original position
when released. Inspect the heater hose to
make sure it is installed properly and in good condition.
1. Allow the genset to cool down. The temperature
inside the housing must be the same as the
ambient temperature.
2. Loosen the adjustment screw holding the adjustment
plate.
3. Slowly rotate the adjustment plate until the bimetal
choke shaft connection is visible in the
sight window. This is the correct setting for an
ambient temperature of 70° F (21° C).
If the ambient temperature is higher or lower
than 70° F (21° C), make a mark on the
choke coil housing opposite the center mark
on the adjustment plate. Each mark on the
adjustment plate is equal to 10° F (6° C) of
difference from 70° F (21° C). If it is warmer
than 70° F (21° C), rotate the plate clockwise.
If the temperature is less than 70° F (21° C),
rotate the plate counterclockwise. Tighten the
adjustment screw.
Example: If the ambient temperature is 90° F
(32° C), rotate the adjustment plate two
marks clockwise from the 70° F (21° C) position
marked on the housing.
4. Move the choke lever back and forth to check
for free movement. Verify that the choke does
not bind or stick.
Bimetal Coil Replacement: After making the
choke adjustment, start the genset and observe engine
operation. If the choke does not open properly,
replace the bimetal coil in the choke housing as follows.
1. Remove the adjustment screw and washer
from the choke coil housing.
2. Remove the housing. Straighten the tab from
the adjustment plate to release the bimetal coil.
3. Remove choke linkage from the bimetal coil
and install linkage on the new coil.
4. Assemble the new coil to the adjustment plate
and bend the tab on the adjustment plate to secure
coil.
5. Install choke coil housing and secure with
screw and washer. Perform the choke adjustment
procedure.
