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John Deere L120 Troubleshooting

The John Deere L120 lawn tractor was manufactured between 2003 and 2005. The John Deere L120 tractor can be powered by two engines: 40.03 cu.in (656 cc) Briggs and Stratton 406777 4-cycle V-twin cylinder OHV vertical-shaft air-cooled gasoline engine with a rated power of 20 hp (15.4 kW), or 40.03 cu.in (656 cc) Briggs and Stratton 407777 4-cycle V-twin cylinder OHV vertical-shaft air-cooled gasoline engine with a rated power of 22 hp (16.4 kW).

The John Deere L120 is equipped with Tuff Torq K46 HD belt-driven hydrostatic transmission with foot-controlled variable speed drive. Max forward speed - 5.5 mph (8.8 km/h), maximum reverse speed - 3.2 mph (5.1 km/h). The lawn tractor is equipped with a manual steering system, wet disc brakes, 16x6.50-8 front tires, and 22x9.50-12 rear tires.

The wheelbase is 49" (1240 mm). The John Deere L120 is compatible with a 42" mid-mount 2-blade mower deck with cutting height of 1.0-4.0" (25-102 mm) and manual lift system, 42" front-mount dual-stage snowblower with clearing height of 21" (530 mm), and 46" front blade with lift height of 6.5" (160 mm).

Engine Troubleshooting
Engine starts hard or will not start
No fuel in fuel tank - Fill it up
Wrong grade of gasoline - Use quality fuel
Clogged fuel system - Remove clogging
Loose or disconnected spark plug wire - Check the spark plug wire connection, repair or replace
Spark plug is damaged - Change spark plug as required
Plugged fuel filter - Change fuel filter
Brake pedal not depressed - Press the brake pedal
Carburetor not adjusted - Adjust according to instructions
Engine has bad compression - Check cylinder block and change wear parts
Not adjusted or damaged throttle cable - Change cable or adjust properly
Engine runs roughly
Air intake grill is clogged - Wash or clean as required
Ignition system malfunction - Inspect ignition system and change failed components
Stuck or defective throttle cable - Replace or service the cable
Air filter element is plugged - Change or service air filter
Fuel pump is dirty or defective - Service or change fuel pump
Engine starts but then stalls
Damaged spark plug - Replace spark plug
Carburetor is faulty or clogged - Replace or service carburetor
Ignition coil is not working - Change ignition coil as required
Broken or bad valve springs - Valve springs need to be changed
Valves sticking - Clean the valves
Engine is overheated
Lack of engine oil - Check and refill engine oil
Engine is under excessive load - Reduce the load
Air intake grill is clogged - Need to clean or wash
Carburetor fuel mixture is too lean - Set the carburetor correctly
Wrong ignition timing - Set the ignition timing properly
Valve setting is improper - Adjust valves correctly
Engine knocking or noise
Stale fuel - Use proper fuel
Engine is under excessive load - Reduce the load
Engine oil level is insufficient - Fill up the oil to required level
Low idle speed set incorrectly - Correct the settings
Dirty or damaged fuel pump - Test fuel pump and change if necessary
Crankshaft or main bearings are worn out - Install new parts as as required
Valve clearance is improper - Need to adjust valve clearance
Damaged cylinder bore or piston rings - Change defective components
Engine power is too low
Carburetor is dirty or improperly adjusted - Service or properly adjust carburetor
Plugged air filter - Clean or change air filter
Fuel pump is clogged or faulty - Check fuel pump and change if required
Ignition system is defective - Check ignition system and replace faulty parts
Cylinder head gasket is damaged - Replace the head gasket
Valves are burned or stuck - Replace or service valves
Worn or defective push rod - Push rod needs to be changed
Cylinder block components are damaged - Change defective components
Engine uses too much fuel
Choke opening is not full - Replace or adjust choke cable
Incorrect adjustment of carburetor main jet - Adjust it correctly
Loose or faulty spark plug - Tighten or change the spark plug
Stuck, worn, or burned valves - Replace or clean valves
Rings, sleeve, or piston are damaged - Change faulty components
Excessive valve clearance - Adjust valve clearance according to specifications
High oil consumption
Damaged gaskets or seals - New components need to be installed
Valve guides and stems are worn - Need to replace the valves
Worn or stuck piston rings - Install new piston rings
Cylinder liner or piston is worn - Inspect liner and piston, change as necessary
Plugged breather pipe or hose - Replace or clean

Hydrostatic Transmission Troubleshooting
HST transmission makes noise
Defective or not adjusted speed control pedal linkage - Change or adjust linkage
Excessive loading - The load should be reduced
Transmission fluid is dirty or fluid level is too low - Add fluid to correct level or fill the transmission with fresh fluid
Worn or defective parts of transmission - Check transmission components and change if necessary
Shifting is hard
Corroded or worn shift linkage - Lubricate or change linkage
Hydrostatic pump is worn or stuck - Replace or repair pump
Faulty or misadjusted transmission shift control parts - Adjust properly or change
Low power
Insufficient transmission fluid - Check and refill the transmission fluid
Worn or damaged drive sheave - Replace sheave
Unadjusted or broken shift linkage - Adjust properly or change linkage
Worn or out of adjustment speed control linkage - Adjust or replace linkage
Transmission leakage
Transmission seals or gaskets are broken - Seals and gaskets need to be replaced
Final drive shaft leaks - Replace shaft seals
Cracked transmission case - Replace defective case or transmission assembly

Mower Deck Troubleshooting
Mower vibrates too much
Mower deck drive sheave is clogged or worn - Clean or change sheave
Drive belt is defective or loose - Install a new belt or adjust belt tension
Mower blades are unbalanced or bent - Balance or replace blades
Blade bolts are not tightened well - Tighten bolts as required
Discharge chute regular clogging
Mowing speed is too high - Use a lower speed
Grass is too long - Use a lower cutting height
Low engine speeds - Open choke fully
Cutting height is too low - Change cutting height adjustment
Improper drive belt installation - Install drive belt as required
Lawn mower leaving uncut grass
Deck is plugged with grass - Clean out the mower deck
Blades are not sharp - Need to sharpen the blades
Damaged or worn blades - Replace the blades
Mowing speed is too high - Operate at slower speed
Cutting level is too low - Change cutting height adjustment
Full bagger - Remove grass from bagger
Blades are scalping the grass
Bumpy or not smooth lawn - Level the lawn
Cutting height is too low - Change cutting height adjustment
High ground speed - Use a lower speed
Deck level is not correct - Level the deck properly
Damaged or bent blades - Blades must be changed
Low tire pressure - Correct tire pressure
Uneven cutting
Incorrect tire pressure - Inflate tires as required
Improperly leveled mower deck - Deck needs to be adjusted properly
Blades are too dull - Blades need to be sharpened
Worn or defective blades - Blades must be changed
Discharge chute is plugged - Need to clean the mower deck
Deck shell is broken - Replace or rebuild mower deck
Bent or loose mower spindle - Change or repair the spindle

Electrical Troubleshooting
Battery cannot be charged
Corroded or loose wire connections - Clean or tighten connections
Faulty battery terminal connectors - Replace terminal connectors
Battery faulty cell - Battery change required
Starter turns slowly
Low battery output - Recharge the battery
Battery runs out quickly - Service charging system or change battery
Terminals are faulty or battery cables are disconnected - Check cables and change or clean terminals
Starter motor won't turn
Battery is low or faulty - Change or recharge battery
Battery wiring is disconnected or improperly connected - Inspect wiring and connect as required
Low battery power - Low battery charging, charge as required
Spark plug faulty or incorrectly gapped - Clean, gap or replace spark plug
Solenoid or starter motor failure - Repair starter or replace solenoid




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