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John Deere D125 Troubleshooting

The John Deere D125 lawn tractor was manufactured from 2014 to 2017. The JD D125 powerline components: Briggs and Stratton 40R877 4-cycle V-twin cylinder OHV air-cooled gasoline engine and Tuff Torq T40 belt-driven hydrostatic transmission with infinite forward and reverse gears.

A 40.1 cubic inches (655 cc) engine has a cylinder bore of 2.97" (75 mm), piston stroke of 2.89" (73 mm), and rated power of 20 hp (14.9 kW). Max. forward speed - 5.5 mph (8.8 km/h), maximum reverse speed - 3.2 mph (5.1 km/h).

The John Deere D125 is equipped with a manual steering system, disc brakes, 15x6.00-6 front tires, and 20x8.00-8 rear tires. The wheel base is 49" (1240 mm). The lawn tractor is compatible with the following attachments: 42" mid-mount 2-blade mower deck with cutting height of 1-4" (25-102 mm), 43.25" front-mount 2-stage snowblower with clearing height of 18" (450 mm), and 46" front blade with mechanical lift system.

Engine Troubleshooting
Engine will not start or starts up hard
No gasoline in tank - Fill fuel up
Wrong grade of gasoline - Use quality gasoline
Water or air in fuel system - Remove air or water from system
Defective spark plug wire connection - Inspect the spark plug wire connection, replace or repair
Spark plug is defective - Change spark plug
Fuel filter is plugged - Change fuel filter
Brake pedal not pushed down - Push the brake pedal down
Carburetor components worn out - Repair or replace parts
Low cylinder compression - Check cylinder block and replace worn parts
Improperly adjusted or worn throttle cable - Adjust properly or change the cable
Engine runs unevenly
Clogged cooling fins - Need to wash or clean
Ignition system failure - Check ignition system and replace faulty parts
Stuck or faulty choke cable - Clean or replace the cable
Air filter element is plugged - Replace or clean air filter
Dirty or defective fuel pump - Clean or install new fuel pump
Engine starts and stalls immediately
Faulty spark plug - Replace spark plug
Clogged or defective carburetor - Service or change carburetor
Ignition coil is not working - Change ignition coil as required
Loose or broken valve springs - Install new valve springs
Valves are stuck - Valves must be cleaned
Engine keeps overheating
Not enough engine oil - Fill the crankcase with engine oil
Engine is overloaded - Load reducing is recommended
Cooling fins are plugged - Clean and wash as required
Carburetor mixture is too lean - Use proper settings
Ignition timing is wrong - Set the ignition timing correctly
Valve setting is improper - Set the valves correctly
Engine knocking sound or abnormal noise
Stale or low octane fuel - Use proper gasoline
Engine overloaded - Reduce engine load
Engine oil level low - Add oil to the engine crankcase
Low idle speed set incorrectly - Test and adjust
Fuel pump is faulty or clogged - Clean or install new fuel pump
Main bearings or crankshaft wear - Change or repair worn components
Excessive valve clearance - Need to adjust valve clearance
Piston rings or cylinder bore are damaged - Replace defective components
Loss of engine power
Carburetor is incorrectly adjusted or clogged - Clean or correctly adjust carburetor
Dirty air filter element - Change or service air filter
Clogged or defective fuel pump - Test fuel pump and change if necessary
Ignition failure - Check ignition and replace faulty components
Cylinder head gasket is blown - Replace cylinder head gasket
Valves are burned or stuck - Change or service valves
Push rod is worn or defective - Replace push rod
Cylinder block parts are damaged - Defective parts need to be replaced
Engine using too much gasoline
Insufficient choke opening - Inspect choke cable and adjust as required
Improper carburetor main jet adjustment - Adjust it properly
Spark plug is loose or defective - Spark plug need to be tightened or replaced
Valves are stuck, worn, or burned - Replace or clean valves
Sleeve, piston, or rings are damaged - Replace defective components
Valve clearance is not correct - Need to adjust valve clearance
Excessive oil consumption
Defective seals or gaskets - Install new components
Damaged valve stems or valve guides - Change the valves
Piston rings are seized or worn - Piston rings replacement required
Scuffed piston or cylinder liner - Inspect piston and liner, replace as required
Breather hose or pipe is blocked - Service or replace

Hydrostatic Transmission Troubleshooting
HST transmission noise
Speed control linkage is worn or unadjusted - Adjust or replace linkage
Transmission overload - Reduce loading
Transmission fluid is dirty or fluid level is too low - Pour fresh fluid or add transmission fluid to proper level
Worn or defective transmission components - After disassembly and inspection, replace defective components
Difficult shifting
Shift linkage is rusty or worn - Lubricate or replace the linkage
Hydrostatic pump is blocked or defective - Change or repair pump
Unadjusted or damaged transmission shift control parts - Adjust correctly or replace
Loss of power
Transmission fluid insufficient - Need to add transmission fluid
Drive pulley is worn or faulty - Replace pulley
Shifter linkage is faulty or not adjusted - Adjust properly or replace linkage
Worn or out of adjustment speed control linkage - Adjust or repair linkage
Transmission leaks
Damaged transmission seals or gaskets - Seals and gaskets need to be replaced
Final drive shaft leaks - Replace shaft seals
Cracked transmission housing - Install a new transmission housing

Mower Deck Troubleshooting
Mower vibrates too much
Mower deck drive pulley is worn or dirty - Clean or change pulley
Loose or damaged drive belt - Adjust belt tension or replace belt
Warped or not balanced mower blades - Balance or change as needed
Blade mounting bolts are loose - Bolts need to be tightened
Constant clogging of discharge chute
Ground speed is too fast - Operate at slower speed
Tall grass - Adjust mower to lower cutting height
Reduced engine speeds - Open choke fully
Mower cuts too low - Change cutting height adjustment
Drive belt installation is not correct - Install drive belt correctly
Lawn mower leaving uncut grass
Discharge area is clogged - Need to clean the mower deck
Not sharp blades - Need a blade sharpening
Worn or damaged blades - Replace the blades
High mowing speed - Operate at slower speed
Cutting level is too low - Must be set to high cutting height
Bagger is full - Clean bagger
Blades are scalping the grass
Lawn is not level or bumpy - Lawn leveling required
Low cutting height - Raise the cutting height
Ground speed is too fast - Use a slower speed
Improperly leveled mower deck - Level the deck correctly
Blades are worn or bent - Replace the blades
Tires are not properly inflated - Correct tire pressure
Mower cuts uneven
Tire pressure is too low - Inflate tires as required
Improperly leveled mower deck - Adjust the level of mower deck correctly
Blades are excessively dull - Need a blade sharpening
Blades are defective or worn - Blades must be changed
Cutting deck is clogged - Clean mower deck as required
Damaged mower deck shell - Repair or change the deck
Loose or faulty mower spindle - Change or repair the spindle

Electrical Troubleshooting
Battery does not charge
Loose or corroded electrical wiring connections - Tighten or clean electrical wiring connections
Electrical terminal connectors are faulty - Terminal connectors should be replaced
Battery failing - Replace the battery
Starter turns slow
Low battery power - Battery is drained, recharge it
Battery won’t hold charge - Service battery or change it
Disconnected wiring or bad battery terminals - Connect wiring properly or install new terminals
Starter is not working
Battery is low or faulty - Recharge or replace battery
Wiring is incorrectly connected or disconnected - Inspect wiring and connect correctly
Battery capacity is low - Battery is drained, recharge it
Incorrectly gapped or worn spark plug - Clean, gap or replace spark plug
Starter motor or solenoid is defective - Starter/solenoid needs to be replaced




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