Cleaning And Storage; Troubleshooting Chart; Specifications - MTD MP425 Operator's Manual

4-cycle trimmer

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Operator's manual (72 pages)

Table Of Contents

Table of Contents

Available languages

Enlarged version

MAINTENANCE AND REPAIR INSTRUCTIONS

• 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 you

clean or service it.

This service requires disassembly of the engine. If feeling unsure or unqualified to perform this service, take the unit to

an authorized service center.

NOTE:

Inspect the valve to rocker arm

clearance with a feeler gauge after the

first 10 hours of operation and every 25

hours of operation.

• 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 five (5) screws with a Flat-head or

T-20 Torx screwdriver and the one T-25 screw

(Fig. 39).

2. Disconnect the spark plug wire.

3. Clean dirt from around the spark plug. Remove

the spark plug from the cylinder head by

turning a 5/8 in. socket counterclockwise.

4. Remove the engine cover (Fig. 39).

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. 40). 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. 40).

• 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. 41). Measure both the intake and exhaust valves.

The recommended clearance for both intake and exhaust is .003 – .006 in. (.076 – 0.152 mm). Use a standard

automotive .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. See Figures 41 and 42.

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. 42).

• 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 791-180852B or Champion #RDZ19H spark plug. The correct air gap is 0.025 in. (0.635

mm.). Remove the plug after every 25 hours of operation and check its condition.

1. Stop the engine and allow it to cool. Remove the five (5) screws with a Flat-head or T-20 Torx screwdriver and the

one T-25 screw (Fig. 39).

2. Grasp the plug wire firmly and pull the cap from the spark plug.

WARNING: Do not sand blast, scrape or clean electrodes. Grit in the

engine could damage the cylinder.

3. Clean dirt from around the spark plug. Remove the spark plug from the cylinder

head by turning a 5/8 in. socket counterclockwise.

4. Replace cracked, fouled or dirty spark plug. Set the air gap at 0.025 in. (0.635 mm)

using a feeler gauge (Fig. 43).

5. 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.

SPARK ARRESTOR MAINTENANCE

1. Remove the rear engine cover. See Rocker Arm Clearance.

2. With a flat blade screwdriver or Torx T-20 bit and a T-25 bit, remove the screws

attaching the spark arrestor cover to the muffler (Fig. 44).

3. Pull the tab on the spark arrestor cover out of the muffler. Remove the spark

arrestor cover.

4. Remove the spark arrestor screen from the spark arrestor cover.

5. Clean the spark arrestor screen with a wire brush or replace it.

6. Reinstall the spark arrestor screen, spark arrestor cover and screws.

CLEANING

WARNING:

To avoid serious personal injury, always turn the unit off and allow it to cool before

cleaning or servicing it.

Use a small brush to clean off the outside of the unit. Do not use strong detergents. Household cleaners that contain

aromatic oils such as pine and lemon, and solvents such as kerosene, can damage plastic housing or handle. Wipe off

any moisture with a soft cloth.

STORAGE

• Never store the unit with fuel in the tank where fumes may reach an open flame or spark.

• Allow the engine to cool before storing.

• Lock up the unit to prevent unauthorized use or damage.

• Store the unit in a dry, well-ventilated area.

• Store the unit out of the reach of children.

LONG TERM STORAGE

1. Drain all gasoline from the gas tank into a container. Do not use gas that has been stored for more than 60 days.

Dispose of the old gasoline in accordance to Federal, State, and Local regulations.

2. Start the engine and allow it to run until it stalls. This ensures that all gasoline has been drained from the carburetor.

3. Allow the engine to cool. Remove the spark plug and put 5 drops of high quality motor oil into the cylinder. Pull the

starter rope slowly to distribute the oil. Reinstall the spark plug.

NOTE:

Remove the spark plug and drain all of the oil from the cylinder before attempting to start the trimmer after

storage.

4. Change the oil, referring to Changing the Oil. Dispose of the old oil in accordance to Federal, State and Local

regulations.

5. Thoroughly clean the unit and inspect for any loose or damaged parts. Repair or replace damaged parts and

tighten loose screws, nuts or bolts. The unit is ready for storage.

TRANSPORTING

• Allow the engine to cool before transporting.

• Secure the unit while transporting.

• Drain the gas tank before transporting.

• Tighten gas cap before transporting.

View Of The Rear Engine Cover

Rocker Arm

Cover

Screws

Spark

Plug Hole

T-25 Screws

Fig. 39

Adjustment

Nuts

Intake

Rocker

Arms

0.003–0.006 in.

(0.076–0.152 mm)

Exhaust

Fig. 41

0.025 in.

(0.635 mm.)

Muffler

Spark Arrestor Screen

Slot

T-20 Screw

ENGINE WILL NOT START

CAUSE

Empty fuel tank

Primer bulb wasn't pressed enough

Old fuel

Fouled spark plug

Plugged spark arrestor

ENGINE WILL NOT IDLE

CAUSE

Air filter is plugged

Old fuel

Improper carburetor adjustment

ENGINE WILL NOT ACCELERATE

CAUSE

Fig. 40

Old fuel

Cutting attachment bound with grass

Feeler

Dirty air filter

Gauge

Plugged spark arrestor

ENGINE LACKS POWER OR STALLS WHEN CUTTING

CAUSE

Old fuel

Valve Stem

Fouled spark plug

Plugged spark arrestor

Fig. 42

CUTTING ATTACHMENT WILL NOT ADVANCE LINE

CAUSE

Cutting attachment bound with grass

Cutting attachment out of line

Inner reel bound up

Cutting head dirty

Line welded

Line twisted when refilled

Not enough line is exposed

CUTTING LINE ADVANCES UNCONTROLLABLY

CAUSE

Oil, cleaner or lubricant in cutting head

If further assistance is required, contact an authorized service dealer.

ENGINE*

Engine Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air-Cooled, 4-Cycle

Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 cu. in. (26.2 cc)

Operating RPM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,200+ rpm

Idle Speed RPM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,800 - 3,600 rpm

Ignition Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electronic

Ignition Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rocker Switch

Valve clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.003–0.006 in. (0.076–0.152 mm)

Spark Plug Gap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.025 inch (0.655 mm)

Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAE 30 Oil

Crankcase Oil Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.04 oz (90 ml)

Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unleaded

Fig. 43

Carburetor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diaphragm, All-Position

Starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Auto Rewind

Muffler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Baffled with Guard

Throttle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manual Spring Return

Fuel Tank Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 oz (532 ml)

DRIVE SHAFT AND CUTTING ATTACHMENT*

Diverter

Drive Shaft Housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Tube (EZ-Link™)

T-25

Throttle Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Finger-Tip Trigger

Screw

Total Approximate Unit Weight (without fuel) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5-13.0 lbs (5.2-5.9 kg)

Cutting Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bump Head™ w/SpeedLock™

Line Spool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bump Line Releaser

Fig. 44

Line Spool Diameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 inches (101.6 mm)

Trimming Line Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.095 inches (2.41 mm)

Cutting Path Diameter, Trimmer Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 inches (43.2 cm)

*All specifications are based on the latest product information available at the time of printing. We reserve the right to

make changes at any time without notice.

TROUBLESHOOTING

ACTION

Fill fuel tank with fuel

Press primer bulb fully and slowly 10 times

Drain gas tank and add fresh fuel

Replace or clean the spark plug

Clean or replace spark arrestor

ACTION

Replace or clean the air filter