Engine Speed Governor

throttle lever and choke lever. They must operate

(a) Adjust the throttle control of the

freely, without binding. Refer a damaged carburetor to

pump to open the carburetor throttle to about one-fourth

direct support maintenance.

open.

d. Installation. Install the carburetor by reversing

(b) Turn the main adjusting screw

the removal procedure. Note the following:

clockwise to reduce the fuel to the engine until the

engine begins to miss due to a lean fuel mixture.

(1) Make sure there are no air leaks between

the carburetor and air cleaner. Air leaks will allow dust

(c) Turn

the

adjusting

screw

and dirt to enter the engine, causing rapid engine wear.

counterclockwise until the engine runs smoothly without

missing.

(2) Adjust the choke wire connection to the

carburetor so that the choke lever can move through its

(3) Adjust the idle mixture adjustment needle

full operating range as the choke control on the

(4, fig. 4-12). This adjustment controls the amount of

instrument panel is operated.

air admitted to the idling system which functions only at

low speeds. Adjust as follows:

(3) Adjust the throttle linkage from the

governor as directed in paragraph 4-25.

(a) With the engine at idle, turn the idle

4-25. Engine Speed Governor

mixture adjustment screw clockwise to cut off air,

making the fuel mixture richer until the engine starts to

a. Adjustment. Adjust the engine speed governor

run roughly due to excessively rich mixture.

as follows:

(b) Turn

the

adjustment

needle

(1) Start the engine and allow it to warm up to

counterclockwise to obtain the smoothest idle operation

operating temperature. While it is warming up, back out

possible.

the surge adjusting screw (9, fig. 4-13) so that it will not

influence the governor setting.

(c) If a vacuum gage is available, use a

vacuum gage attached to the intake manifold and adjust

(2) With the engine warmed up and with the

the needle for highest engine vacuum.

pump not under load, adjust the engine idle speed to

approximately 150 rpm higher than the required idle

(4) Adjust the idle speed adjustment screw (2,

speed under load. Make this adjustment by turning the

fig.

4-12).

Turn the screw clockwise or

speed adjusting screw (11). Back out speed adjusting

counterclockwise as necessary to provide 400 to 600

lock screw (10) so that it will not influence the

rpm idle speed when the pump throttle control is set to

adjustment.

idle.

(3) The governor's range of action is the

b. Removal. Remove the carburetor from the

differential between the engine speed under load and

engine as follows:

the engine speed without load. To broaden the range of

(1) Disconnect the choke control wire (44, fig.

action, use the sensitivity adjusting screw (12).

4-11) from the carburetor choke lever.

Lengthen the sensitivity adjusting screw to broaden the

(2) Disconnect the throttle control wire (45)

range of action of the engine. Compensate for speed

from the carburetor throttle lever.

changes by readjusting the speed adjusting screw (11).

(3) Disconnect the fuel lines from the

To narrow the range of action, shorten the sensitivity

carburetor (para 4-22b).

adjusting screw (12) and compensate for speed change

(4) Disconnect the air cleaner hose from the

with the speed adjusting screw (11).

carburetor (para 4-18b).

(4) When the governor range of action is

(5) Disconnect the carburetor bowl drain hose

properly adjusted, allow the engine to run at governed

(5) from the carburetor.

speed, no load, and check for surging. If surging is

noted, turn in the surge adjusting screw (9) just far

(6) Remove the nuts (21) and lock washers

enough to eliminate the surging.

(22) that secure the carburetor to the intake manifold;

remove the carburetor and gasket.

(5) The surge adjustment can also be

adjusted by using the tachometer. With the engine

c. Cleaning and Inspection.

running at governed speed, no load, turn the surge

(1) Clean the exterior of the carburetor with a

adjusting screw (9) in until the engine speed increases

cloth dampened with cleaning solvent (fed. spec. P-D-

10 to 20 rpm and tighten the

680) ; dry thoroughly.

(2) Inspect the carburetor for cracks and

other obvious damage. Check the operation of the

4-16