Choke Unloader Adjustment; Curb Idle Adjustment; Erratic Engine Idle/Low Idle Speed Adjustment; Fast Idle Adjustment - Ford LSG 875 Service Manual

3-35
FUEL SYSTEM
3-35
MODEL 4160 CARBURETOR SYSTEMS (Continued)
CHOKE UNLOADER ADJUSTMENT
DRILL INSERTED B
The choke unloader is a mechanical device to
OF AIR HORN AND
partially open the choke at wide open throttle. It
is used to eliminate choke enrichment during
cranking of an engine. Engines which have been
flooded or stalled by excessive choke enrich-
ment can be cleared by use of the unloader. Ad-
just the system as follows:
1. Qualify the choke control lever, if necessary.
2. Hold the throttle valves in the wide open
position. Insert the specified drill shank or
gauge between the upper edge of the choke
valve and inner wall of air horn.
3. With g finger lightly pressing against the
choke control lever or plate, a slight drag
should be felt as the gauge is withdrawn. If
an adjustment is necessary, bend the indi-
cated throttle lever tang until correct opening
has been obtained.
CURB IDLE ADJUSTMENT
Connect tachometer to engine, tachometer
should have 1 l/2 to 2 l/2 accuracy and an ex-
panded scale of l-1000 R.P.M. or 400-800
R.P.M.
1. Adjust the idle mixture screws fully in until
they are lightly seated. Back them out 1 l/2
revolutions. This will provide sufficient ad-
justment to be able to start the engine.
2. Be sure the engine is thoroughly warmed
up. Adjust the curb idle speed to specifica-
tion by turning the throttle stop screw " in" to
increase idle speed, or " out" to decrease
idle speed.
cylinder or occasional misfire will turn an en-
gine that is a minor emitter into gross
emitter.
2. Check for vacuum leaks (vacuum lines or
manifold).
LOW IDLE SPEED ADJUSTMENT
With engine at correct operating temperature
and condition as in above procedure and curb
idle adjusted to specifications, proceed as
follows:
1. Set the low idle speed to specifications by
adjusting the low idle speed adjusting screw.
3. Turn the idle mixture adjustment screws in-
ward until the engine speed begins to drop
due to a lean mixture. Next, turn the screws
outward until the engine speed begins to
drop due to an excessively rich mixture.
Then, turn the screws inward to a point be-
tween these two extremes to obtain max-
imum engine smoothness and rpm.
4. Reset idle speed to specifications.
5. Recheck idle mixture adjustment and reset if
necessary.
6. Disconnect tachometer from engine.
FAST IDLE ADJUSTMENT
1. Remove air cleaner.
2. Attach tachometer.
3. With engine off and at normal operating
temperature, transmission in neutral, open
throttle, and close the choke.
4. Close throttle, then release choke to place
fast idle screw on highest speed step. Move
fast idle cam until screw drops down to sec-
ond step of the cam against the first step
shoulder.
ERRATIC ENGINE IDLE
If the engine idle is erratic or rough after cor-
rect idle adjustment, check the following items:
1. Recheck spark plugs and spark plug wires.
Be sure all cylinders are firing. A missing
5. Without touching throttle, start engine, allow
engine speed to stabilize and observe ta-
chometer. Engine should operate at spec-
ified fast idle speed. Readjust fast idle screw
if necessary.