Murray MX550 Lawn Mower Manual

The Murray MX550 is a 21-inch push lawn mower featuring a 140cc Briggs & Stratton engine, 3-in-1 mulching/bagging/side-discharge capability, single-lever height adjustment (6 positions: 1.25"-3.75"), durable steel deck, easy-start system, washout port for cleaning, and large rear wheels for better maneuverability. This manual covers safety, assembly, operation, maintenance, troubleshooting, and storage procedures to ensure optimal performance and longevity.

1. Features at a Glance 2. Assembly Instructions 3. Safety Precautions 4. Specifications 5. Controls and Operation 6. Cutting Height Adjustment 7. 3-in-1 Function Setup 8. Maintenance Schedule 9. Storage & Winterization 10. Warranty Information 11. Troubleshooting

Features at a Glance

Key components: 140cc Briggs & Stratton engine, 21-inch steel cutting deck, rear grass bag, mulch plug, side discharge chute, single-lever height adjuster, washout port, and push handle.

Feature	Description
Engine	140cc Briggs & Stratton 4-cycle, easy-start system
Cutting Width	21 inches
Cutting Height	6 positions (1.25" to 3.75")
Deck Material	Durable powder-coated steel
3-in-1 Function	Mulch, Bag, or Side Discharge
Wheels	Large 8-inch rear wheels for easy pushing
Handle	Foldable for compact storage
Washout Port	For easy deck cleaning after use
Fuel Tank	0.5-gallon capacity
Weight	Approximately 55 lbs

Assembly Instructions

Unpack all parts from the box. Assembly requires basic tools (included).

Attach the handle: Align lower handle with deck brackets, secure with provided bolts and wrench.
Install the upper handle: Connect to lower handle, tighten knobs.
Attach the grass bag: Hook bag frame onto rear deck brackets.
Install side discharge chute (if needed): Snap into place on right side of deck.
Insert mulch plug (for mulching): Place into rear discharge opening.
Check wheel height: Ensure all wheels are set to same position.
Add oil and fuel: Use SAE 30 oil (approx. 20 oz) and unleaded gasoline (87 octane or higher).

WARNING! Do not add fuel indoors or near ignition sources. Ensure all bolts are tight before operation.

Safety Precautions

Always follow safety guidelines to prevent injury or damage.

Read manual thoroughly before use.
Wear sturdy shoes, long pants, and eye protection.
Clear mowing area of stones, sticks, and debris.
Never mow wet grass or in rain.
Keep hands and feet away from moving parts.
Stop engine before adjusting height or clearing blockages.
Do not allow children to operate mower.
Use outdoors only; ensure proper ventilation.

CAUTION! Gasoline is flammable. Store fuel in approved container away from heat sources.

Specifications

Model: Murray MX550
Engine: Briggs & Stratton 140cc 4-cycle
Cutting Width: 21 inches
Cutting Height Range: 1.25" - 3.75" (6 positions)
Deck: 21-inch steel, powder-coated
Wheels: 8-inch rear, 7-inch front
Fuel Type: Unleaded gasoline (87 octane or higher)
Oil Type: SAE 30 (20 oz capacity)
Bag Capacity: 1.8 bushels
Warranty: 2-year limited warranty

Controls and Operation

Handle Controls: Throttle lever, recoil starter grip, blade control bar (deadman's switch).

Starting Procedure:

Check oil and fuel levels.
Push throttle lever to FAST position.
Prime engine (press primer bulb 3 times if cold).
Pull recoil starter grip firmly.
Once started, adjust throttle as needed.

Stopping: Release blade control bar, move throttle to STOP, wait for blade to stop completely.

Blade Control: Must be held against handle to keep blade engaged. Release to stop blade instantly.

Cutting Height Adjustment

Single-lever adjustment changes height for all four wheels simultaneously.

Stop engine and ensure blade is not moving.
Pull height adjustment lever toward wheel.
Move lever to desired position (1-6, where 1 is lowest).
Release lever to lock into place.
Check that all wheels are at same height.

Tip: For first mow of season, set to highest position. Gradually lower for subsequent mows.

3-in-1 Function Setup

Configure mower for mulching, bagging, or side discharge.

Mulching: Install mulch plug in rear discharge opening. Grass is cut finely and returned to lawn as fertilizer.
Bagging: Remove mulch plug, attach grass bag to rear brackets. Collects clippings for disposal.
Side Discharge: Remove mulch plug and bag, attach side discharge chute. Ejects clippings to side (right).

WARNING! Always stop engine before changing configuration. Ensure attachments are securely installed.

Maintenance Schedule

Maintenance Task	Frequency
Check oil level	Before each use
Check blade sharpness/condition	Every 25 hours
Clean under deck	After each use
Replace air filter	Every season or 25 hours
Change oil	First 5 hours, then every 50 hours
Replace spark plug	Every 100 hours
Lubricate wheels and height adjuster	Every season
Inspect/replace drive belt (if equipped)	Every 2 seasons

Blade Sharpening: Remove blade, sharpen at 30-degree angle, balance before reinstalling.

Storage & Winterization

Proper storage extends mower life.

Run engine to use up fuel or add fuel stabilizer.
Change oil and replace air filter.
Clean entire mower, especially under deck.
Remove spark plug, add 1 teaspoon oil, pull starter slowly to coat cylinder.
Store in dry, covered area away from moisture.
Cover mower to prevent dust accumulation.

CAUTION! Never store mower with fuel in tank indoors or in enclosed spaces due to fire risk.

Warranty Information

Murray MX550 comes with a 2-year limited warranty covering defects in materials or workmanship. Warranty does not cover normal wear, misuse, neglect, or commercial use. Proof of purchase required. For warranty service, contact Murray customer service at 1-800-269-6215 or visit www.murray.com. Keep this manual and receipt for reference.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No fuel, old gas, clogged air filter, spark plug issue	Check fuel level; use fresh gas; clean/replace air filter; check spark plug.
Engine runs poorly	Dirty air filter, old fuel, carburetor issue	Clean air filter; drain old gas; consider carburetor cleaning.
Uneven cutting	Dull blade, uneven tire pressure, deck clogged	Sharpen/replace blade; check tire pressure; clean under deck.
Excessive vibration	Loose blade, bent blade, debris in deck	Tighten blade bolt; replace bent blade; clean deck.
Grass not discharging	Wet grass, deck clogged, dull blade	Mow when dry; clean deck; sharpen blade.
Wheels not turning smoothly	Debris in axles, lack of lubrication	Clean axles; apply light lubricant.

Service: For repairs beyond basic maintenance, contact authorized Murray service center at 1-800-269-6215.