Murray 312008X51 Lawn Mower Manual

The Murray 312008X51 is a 21-inch push lawn mower featuring a 190cc Briggs & Stratton engine, 3-in-1 mulching/bagging/side discharge capability, single-lever height adjustment (6 positions: 1.5-3.75 inches), durable steel deck, easy-start system, and large 2.1-bushel rear bag. This manual covers safety, assembly, operation, maintenance, troubleshooting, and specifications.

1. Features at a Glance 2. Assembly Instructions 3. Safety Information 4. Specifications 5. Controls and Operation 6. Cutting Height Adjustment 7. Maintenance Schedule 8. Storage Guidelines 9. Warranty Information 10. Troubleshooting

Features at a Glance

Key components: 21-inch steel cutting deck, 190cc Briggs & Stratton engine, rear grass bag, single-lever height adjuster, mulching plug, discharge chute, and push handle with safety bail.

Feature	Description
Engine	190cc Briggs & Stratton 675 Series, 4-cycle
Cutting Width	21 inches
Cutting Height	6 positions (1.5 - 3.75 inches)
Cutting Options	Mulch, Bag, Side Discharge
Deck Material	Powder-coated steel
Grass Bag Capacity	2.1 bushels
Starting System	Recoil pull-start
Wheels	8-inch rear, 7-inch front
Weight	Approximately 60 lbs
Fuel Tank Capacity	0.95 quarts

Assembly Instructions

Unpack all parts and inspect for damage. Assembly requires basic tools (included).

Attach handle: Align lower handle with deck brackets, secure with provided bolts and wing nuts.
Install upper handle: Connect to lower handle, tighten knobs.
Attach grass bag: Hook bag frame onto rear deck brackets, ensure secure fit.
Install mulching plug (if using): Place into discharge chute opening.
Add engine oil: Fill with SAE 30 detergent oil (approx. 20 oz) as per engine manual.
Add fuel: Use fresh unleaded gasoline (87 octane minimum).

WARNING! Do not add fuel or oil indoors or near ignition sources. Keep hands clear of cutting blade during assembly.

Safety Information

Read all instructions before operation. Always wear sturdy shoes and eye protection.

Clear mowing area of stones, toys, and debris.
Never mow wet grass or operate on steep slopes.
Do not allow children or pets in area during mowing.
Stop engine and wait for blade to stop before crossing gravel drives or roads.
Never reach under mower deck while engine is running.
Use the safety bail: Release to stop engine and blade within 3 seconds.

CAUTION! Fuel is flammable; store in approved container away from heat. Always disconnect spark plug wire before performing maintenance.

Specifications

Model: Murray 312008X51
Engine: Briggs & Stratton 190cc, 4-cycle, OHV
Cutting Width: 21 inches
Cutting Height Range: 1.5 to 3.75 inches (6 positions)
Deck: 21-inch steel, powder-coated
Wheels: 8-inch rear, 7-inch front
Bag Capacity: 2.1 bushels
Weight: Approx. 60 lbs
Fuel Type: Unleaded gasoline (87 octane or higher)
Oil Type: SAE 30 detergent (summer), 10W-30 (variable temps)

Controls and Operation

Handle Controls: Safety bail (must be held to run), height adjustment lever, push handle.

Starting: 1. Check oil and fuel levels. 2. Push primer bulb 3 times (cold engine). 3. Set throttle to FAST position. 4. Pull recoil starter firmly.

Stopping: Release safety bail to stop engine and blade. For emergency stop, release bail immediately.

Cutting Options: Bagging: Install grass bag. Mulching: Install mulching plug. Side Discharge: Remove bag and plug, attach discharge chute.

Cutting Height Adjustment

Single-lever adjustment: Move lever to one of 6 positions (1=lowest, 6=highest).

Stop engine and wait for blade to stop.
Move lever to desired position (all wheels adjust simultaneously).
Test height on a small area before mowing entire lawn.

Tip: For first mow of season, set to highest setting. Never cut more than 1/3 of grass blade length at once.

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

Maintenance	Frequency
Check engine oil level	Before each use
Clean under deck	After each use
Check blade sharpness/balance	Every 25 hours
Replace air filter	Every season or 25 hours
Change engine oil	First 5 hours, then every 50 hours
Replace spark plug	Every 100 hours
Lubricate wheel bearings	Every season

Blade Sharpening: Disconnect spark plug wire. Remove blade, sharpen at original angle (40°), balance before reinstalling.

Storage Guidelines

Prepare mower for off-season storage to prevent damage.

Run engine to burn remaining fuel or add fuel stabilizer.
Change engine oil.
Clean entire mower, especially under deck.
Remove spark plug, add 1 tablespoon oil to cylinder, pull starter slowly to coat.
Store in clean, dry place, covered to prevent dust.

CAUTION! Never store mower with fuel in tank indoors or in enclosed spaces without proper ventilation.

Warranty Information

Murray mowers are backed by a limited warranty. Residential use: 2-year limited warranty on mower, engine covered by Briggs & Stratton warranty (terms apply). Proof of purchase required. Warranty does not cover normal wear, misuse, or lack of maintenance. For warranty service, contact an authorized Murray service center. Keep this manual and receipt for reference.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No fuel, old fuel, clogged air filter, spark plug	Check fuel level; use fresh gas; clean/replace air filter; check spark plug.
Engine runs poorly	Dirty air filter, old fuel, carburetor issues	Replace air filter; drain old fuel; clean carburetor.
Uneven cutting	Dull blade, uneven tire pressure, deck clogged	Sharpen/balance blade; check tire pressure; clean deck.
Excessive vibration	Loose blade, bent blade, debris in blade	Tighten blade bolt; replace bent blade; remove debris.
Grass not discharging	Wet grass, deck clogged, engine speed too low	Mow when dry; clean deck; run at full throttle.
Wheels not turning freely	Debris in axles, lack of lubrication	Clean axles; lubricate wheel bearings.

Service: For repairs beyond basic maintenance, contact authorized Murray service center. Engine service: Refer to Briggs & Stratton engine manual.

Customer Support: 1-800-269-6215 or www.murray.com