MTD 41ADY21C901 Operator'S Manual Download Page 4

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REPLACING THE TRIMMING LINE

Only use the trimming line described in the Specifications section. Other types of trimming line may
cause the engine to overheat or fail.

NOTE:

Always use the correct line length when installing trimming line. The line may not release

properly if the line is too long.

Part 1 - Removing the Inner Reel

1. Hold the outer spool with one hand and unscrew the bump knob

counterclockwise (Fig. 13).

NOTE:

The outer spool will remain attached to the unit.

2. Inspect the bolt inside the bump knob to make sure it moves freely. Replace

the bump knob if it is damaged.

3. Remove the inner reel from the outer spool (Fig. 14).
4. Remove the spring from the inner reel (Fig. 14).
5. Use a clean cloth to clean the inner reel, spring, shaft and inner surface of

the outer spool.

6. Check the indexing teeth and holding slots for wear (Fig. 15). If necessary,

remove burrs or replace the inner reel and outer spool.

Proceed to Part 2 - Winding New Trimming Line onto the Inner Reel.

Part 2 - Winding New Trimming Line onto the Inner Reel

• If using single line, refer to Winding Single Line.
• If using split line, refer to Winding Split Line.
• If using a prewound inner reel, proceed to

Part 3 - Installing the Inner

Reel

Winding Single Line

1. Cut two 8-foot (2.4 m) lengths of new single trimming line.
2. Insert the end of one line into the top hole in the inner reel (Fig. 16).

Wind the line tightly in the direction shown on the bottom of the inner
reel until about 6 inches (150 mm) of line remains. Keep the line above
the split wall. Insert the 6-inch section into
the nearest .095 holding slot (Fig. 17).

3. Insert the end of the other line into the

bottom hole in the inner reel (Fig. 18).
Wind the line tightly in the direction shown
on the bottom of the inner reel until about
3 to 9 inches (75 to 225 mm) of line
remains. Keep the line below the split
wall. Insert the 3 to 9-inch section into the
opposite .095 holding slot (Fig. 19).

NOTE:

Failure to wind the line in the direction

indicated will cause the cutting head to
operate incorrectly.

Proceed to Part 3 - Installing the Inner Reel.

Winding Split Line

1. Cut one 6-foot (1.8 m) length of new split line

trimming line. Split each end about 6 inches
(150 mm).

2. Using one split end, insert one line into the top

hole and the other line into the bottom hole in
the inner reel (Fig. 20).

3. Wind the line tightly in the direction shown on

the bottom of the inner reel. The split wall will
automatically divide the line. Wind the line until
it is completely divided and about 6 inches
(150 mm) of line remains.

NOTE:

Failure to wind the line in the direction

indicated will cause the cutting head to operate incorrectly.

4. Insert the two 6-inch sections into the two .095 holding slots (Fig. 21).

Proceed to Part 3 - Installing the Inner Reel.

Part 3 - Installing the Inner Reel

1. Pass the two line ends through the eyelets in the outer spool. Place the spring

inside the inner reel. Insert the inner reel into the outer spool. Push the inner
reel and outer spool together (Fig. 22).

NOTE:

The spring must be assembled on the inner reel before reassembling the cutting head.

2. While holding the inner reel and outer spool together, firmly pull the two line ends to release them from the

holding slots.

3. While holding the inner reel and outer spool together, screw the bump knob on clockwise. Tighten the bump

knob securely.

AIR FILTER MAINTENANCE

Cleaning the Air Filter

Failure to maintain the air filter properly can result in poor performance or can cause permanent
damage to the engine.
1. Open the air filter cover by pressing the lock tab in and pulling out on the air filter cover (Fig. 23).
2. Remove the air filter (Fig. 23).
3. Wash the filter in detergent and water. Rinse the filter thoroughly and

allow it to dry.

4. Apply enough clean SAE 30 motor oil to lightly coat the filter.
5. Squeeze the filter to spread and remove excess oil.
6. Replace the air filter into the air filter cover (Fig. 23).

NOTE:

Operating the unit without the air filter

WILL VOID

the warranty.

7. Close the air filter cover by swinging it to the left and then pressing it

down until the lock tab snaps into place (Fig. 23).

IDLE SPEED ADJUSTMENT

The idle speed of the engine is adjustable. An idle adjustment screw is
between the air filter cover and the engine starter housing (Fig. 24).

NOTE:

Careless adjustments can seriously damage the unit. An authorized

service dealer should make carburetor adjustments.

If, after checking the fuel mixture and cleaning the air filter, the engine still
will not idle, adjust the idle speed screw as follows:
1. Start the engine and run for one minute to warm up.

Refer to Starting

and Stopping Instructions.

2. Release the throttle trigger and let the engine idle. If the engine stops, insert a small Phillips screwdriver

into the idle adjustment screw (Fig. 24). Turn the idle speed screw

clockwise

1/8 of a turn at a time (as

needed) until the engine idles smoothly.

3. If the engine appears to be idling too fast, turn the idle speed screw

counterclockwise

1/8 of a turn

at a time (as needed), to reduce idle speed.

Checking the fuel mixture, 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.

WARNING:

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

before you clean or service it.

WARNING:

The cutting attachment will spin during idle speed adjustments. Wear

protective clothing and observe all safety instructions to prevent serious personal injury.

Fig. 23

Air Filter Cover

Air Filter

Lock Tab

Fig. 24

Idle Adjustment Screw

WARNING:

Never use metal-reinforced line, wire, chain or rope. These can break off and become

dangerous projectiles.

MAINTENANCE SCHEDULE

Perform these required maintenance procedures at the frequency stated in the table. These procedures
should also be a part of any seasonal tune-up.

NOTE:

Some maintenance procedures may require special tools or skills. If you are unsure about these

procedures, take your unit to any non-road engine repair establishment, individual or authorized
service dealer.

NOTE:

Maintenance, replacement, or repair of the emission control devices and system may be

performed by any non-road engine repair establishment, individual or authorized service dealer.

NOTE:

Please read the California/EPA statement that came with the unit for a complete listing of terms

and coverage for the emissions control devices, such as the spark arrestor, muffler, carburetor, etc.

MAINTENANCE AND REPAIR INSTRUCTIONS

FREQUENCY

MAINTENANCE REQUIRED

SEE

Before starting engine

Fill fuel tank with fresh fuel

p. 3

Every 10 hours

Clean and re-oil air filter

p. 4

Every 25 hours

Check spark plug condition and gap

p. 4

WARNING:

To prevent serious injury, never perform maintenance or repairs with unit

running. Always service and repair a cool unit. Disconnect the spark plug wire to ensure
that the unit cannot start.

OPERATING INSTRUCTIONS

HOLDING THE UNIT

Before operating the unit, stand in the operating position (Fig. 10). Check
for the following:
• The operator is wearing eye protection and proper clothing
• With a slightly-bent right arm, the operator’s hand is holding the shaft

grip

• The operator’s left arm is straight, the left hand holding the D-handle
• The unit is at waist level
• The cutting head is parallel to the ground and easily contacts the grass without the need to bend over

ADJUSTING TRIMMING LINE LENGTH

The Bump Head™ cutting head allows the release of trimming line without stopping the engine. To release more
line, lightly tap the cutting head on the ground (Fig. 11) while operating the unit at high speed.

NOTE:

Always keep the trimming line fully extended. Line release becomes more

difficult when the cutting line gets shorter.

Each time the head is bumped, about 1 inch (25.4 mm) of trimming line releases. A
blade in the cutting head shield will cut the line to the proper length if any excess
line is released.
For best results, tap the bump knob on bare ground or hard soil. If attempting a line
release in tall grass, the engine may stall. Always keep the trimming line fully
extended. Line release becomes more difficult when the cutting line gets shorter.

NOTE:

Do not rest the Bump Head™ on the ground while the unit is running.

Some line breakage will occur from:
• Entanglement with foreign matter
• Normal line fatigue
• Attempting to cut thick, stalky weeds
• Forcing the line into objects such as walls or fence posts

TIPS FOR BEST TRIMMING RESULTS

• Keep the cutting head parallel to the ground.
• Do not force the cutting head. Allow the tip of the line to do the cutting,

especially along walls. Cutting with more than the tip will reduce cutting
efficiency and may overload the engine.

• Cut grass over 8 inches (200 mm) by working from top to bottom in small

increments to avoid premature line wear or engine drag.

• Cut from right to left whenever possible. Cutting to the left improves the unit's

cutting efficiency. Clippings are thrown away from the operator.

• Slowly move the unit into and out of the cutting area at the desired height. Move either in a forward-backward or

side-to-side motion. Cutting shorter lengths produces the best results.

• Trim only when grass and weeds are dry.
• The life of the cutting line is dependent upon:

• Following the trimming techniques
• What vegetation is being cut
• Where vegetation is cut

For example, the line will wear faster when trimming against a foundation wall as opposed to trimming around a
tree.

DECORATIVE TRIMMING

Decorative trimming is accomplished by removing all vegetation around trees, posts, fences, etc..
Rotate the whole unit so that the cutting head is at a 30° angle to the ground (Fig. 12).

WARNING:

Always wear eye, hearing, foot and body

protection to reduce the risk of injury when operating this unit.

Fig. 10

WARNING:

Do not remove or alter the line cutting blade assembly. Excessive line length

will cause premature engine failure and / or unit damage.

Fig. 11

Fig. 12

MAINTENANCE AND REPAIR INSTRUCTIONS

Fig. 19

Fig. 21