Cub Cadet ST428 Operator's Manual page 11

5. Squeeze the filter to spread and remove
excess oil.
6. Replace the air filter into the base plate
(Fig. 41).
NOTE: If the unit is operated without the air
filter, you will VOID the warranty.
7. Reinstall the air filter cover. Position the two
small tabs on the air filter cover into the two
slots in the back plate and press the air filter
cover down, making sure to align the lock
tab with the lock tab slot, until it snaps into
place (Fig. 39 & 40).
IDLE SPEED ADJUSTMENT
WARNING:
The cutting
attachment may spin during idle
speed adjustments. Wear protective
clothing and observe all safety
instructions to prevent serious
personal injury.
The idle speed of the engine is adjustable. An
idle adjustment screw is between the air filter
cover and the engine starter housing (Fig. 42).
NOTE: Careless adjustments can seriously damage your unit. An
authorized service dealer should make carburetor adjustments.
If, after checking the fuel and cleaning the air filter, the engine still will not
idle, adjust the idle speed screw as follows:
1. Start the engine and let it run at a high idle for a minute to warm up. Refer
to Starting/Stopping Instructions.
2. Release the throttle trigger and let the engine idle. If the engine stops,
insert a small phillips or flat blade screwdriver into the hole in the air
filter/muffler cover (Fig. 42). Turn the idle speed screw in, clockwise, 1/8
of a turn at a time (as needed) until the engine idles smoothly.
NOTE: The cutting attachment should not rotate when the engine idles.
3. If the cutting attachment rotates when the engine idles, turn the idle
speed screw counterclockwise 1/8 of a turn at a time (as needed), to
reduce idle speed.
Checking the fuel, cleaning the air filter, and adjusting the idle speed should
solve most engine problems. If not and all of the following are true:
• the engine will not idle
• the engine hesitates or stalls on acceleration
• there is a loss of engine power
Have the carburetor adjusted by an authorized service dealer.
ROCKER ARM CLEARANCE
WARNING:
To avoid serious
personal injury, always turn the unit
off and allow it to cool before
cleaning or servicing it.
This requires disassembly of the engine. If
feeling unsure or unqualified to perform this,
take the unit to an authorized service center.
• The engine must be cold when checking or
adjusting the valve clearance.
• This task should be performed inside in a
clean, dust free area.
1. Remove the two (2) screws on back of the
engine cover and the one on the front of the
engine cover with a Flat-head or T-25 Torx
screwdriver (Fig. 43).
2. Remove the engine cover (Fig. 44).
MAINTENANCE AND REPAIR INSTRUCTIONS
Air Filter Back Plate
Cover
Fig. 40
Back
Plate
Air Filter
Fig. 41
Idle
Adjustment
Screw
Fig. 42
Remove Screws
Fig. 43
Engine
Cover
Muffler
Fig. 44
3. Disconnect the spark plug wire.
4. Clean dirt from around the spark plug.
Remove the spark plug from the cylinder
head by turning a 5/8 in. socket
counterclockwise.
5. Clean dirt from around the rocker arm cover.
Remove the screw holding the rocker arm
cover with a large flat blade screwdriver or
Torx T-25 bit (Fig. 45). Remove the rocker
arm cover and gasket.
6. Pull the starter rope slowly to bring the
piston to the top of its travel, (known as top
dead center). Check that:
• The piston is at the top of its travel while
looking in the spark plug hole (Fig. 45)
• Both rocker arms move freely, and both
valves are closed
If these statements are not true, repeat this
step.
7. Slide the feeler gauge between the rocker
arm and the valve return spring. Measure the
clearance between the valve stem and
rocker arm (Fig. 47). Measure both the intake
and exhaust valves.
The recommended clearance for both intake
and exhaust is 0.003 – 0.006 in. (0.076 – 0.152
mm). Use a standard automotive 0.005 in.
(0.127 mm) feeler gauge. The feeler gauge
should slide between the rocker arm and valve stem with a slight amount of
resistance, without binding. Figures 46 and 47 show how to measure the
clearance.
8. If the clearance is not within specification:
a. Turn the adjusting nut using a 5/16 inch (8 mm) wrench or nut driver
(Fig. 47).
• To increase clearance, turn the adjusting nut counterclockwise.
• To decrease clearance, turn the adjusting nut clockwise.
b. Recheck both clearances, and adjust as necessary.
9. Reinstall the rocker arm cover using a new gasket. Torque the screw to
20–30 in•lb (2.2–3.4 N•m).
10. Check the spark plug and reinstall. See Replacing the Spark Plug.
11. Replace the spark plug wire.
12. Reinstall the engine cover. Check alignment of the cover before
tightening the screws. Tighten screws.
REPLACING THE SPARK PLUG
Use a replacement part number 753-05784 or Champion® RDZ4H spark
plug. The correct air gap is 0.025 in. (0.635 mm).
1. Stop the engine and allow it to cool. Remove the two (2) screws on back
of the engine cover and the one on the front of the engine cover with a
Flat-head or T-25 Torx screwdriver (Fig. 43).
2. Grasp the plug wire firmly and pull the cap from the spark plug.
3. Clean dirt from around the spark plug. Remove the spark plug from the
cylinder head by turning a 5/8 in. socket counterclockwise.
WARNING:
Do not sand blast,
scrape or clean electrodes. Grit in the
engine could damage the cylinder.
3. Replace cracked, fouled or dirty spark plug.
Set the air gap at 0.025 in. (0.635 mm) using
a feeler gauge (Fig. 48).
4. Install a correctly-gapped spark plug in the
cylinder head. Turn the 5/8 in. socket
clockwise until snug.
If using a torque wrench torque to: 110-120 in.•lb. (12.3-13.5 N•m)
Do not over tighten.
Screw
Rocker Arm
Cover
Spark
Plug Hole
Fig. 45
Adjusting Nuts
INTAKE
Rocker
EXHAUST
Arms
Fig. 46
Rocker Arm
Exhaust
Adjusting
Feeler
Nut
Gauge
0.003–0.006
in.
(0.076–0.152
mm)
Valve Stem
Fig. 47
0.025 in.
(0.635 mm)
Fig. 48
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