Yamaha Grizzly 400 Service Manual

The Yamaha Grizzly 400 is a rugged all-terrain vehicle (ATV) designed for utility and recreational use. This service manual provides comprehensive information for maintenance, repair, and troubleshooting of the Grizzly 400 model. It covers engine specifications, chassis components, electrical systems, periodic maintenance schedules, and detailed repair procedures. Below are key sections for safety, features, maintenance, specifications, and troubleshooting.

1. Features at a Glance 2. Safety Precautions 3. Periodic Maintenance 4. Specifications 5. Engine Service 6. Chassis & Suspension 7. Electrical System 8. Fuel System 9. Drive System 10. Troubleshooting 11. Wiring Diagrams

Features at a Glance

Key components: 400cc air-cooled 4-stroke engine, Ultramatic automatic transmission with engine braking, On-Command 2WD/4WD system, independent rear suspension, front and rear hydraulic disc brakes.

Feature	Description
Engine Type	400cc, 4-stroke, SOHC, air-cooled single cylinder
Transmission	Ultramatic automatic V-belt with all-wheel engine braking
Drive System	On-Command 2WD/4WD with differential lock
Suspension	Independent double wishbone (front), Independent rear suspension (IRS)
Brakes	Hydraulic disc brakes (front and rear)
Fuel Capacity	4.0 gallons (15.1 liters)
Towing Capacity	Up to 850 lbs (386 kg)
Payload Capacity	Up to 176 lbs (80 kg) on rack, 99 lbs (45 kg) on front carrier
Electric Start	Standard with auxiliary recoil starter
Instrumentation	Speedometer, odometer, trip meter, fuel gauge, 4WD indicator

Safety Precautions

Always follow safety procedures when servicing the ATV.

Work in a well-ventilated area away from sparks or flames.
Use proper tools and protective equipment (gloves, safety glasses).
Support the ATV securely on a stand or lift before working underneath.
Disconnect the battery negative terminal before electrical work.
Allow engine to cool before servicing.

WARNING! Gasoline is highly flammable. Do not smoke or use open flames during service. Always relieve fuel system pressure before disconnecting fuel lines.

Periodic Maintenance

Follow the maintenance schedule to ensure optimal performance and longevity.

Pre-ride inspection: Check tires, brakes, lights, controls, and fluid levels.
Engine oil change: Every 100 hours or 6 months (whichever comes first).
Oil filter replacement: Every other oil change.
Air filter cleaning: Every 20 hours; replace if damaged.
Spark plug inspection/replacement: Every 100 hours.
Drive chain adjustment: Check every 20 hours; lubricate regularly.
Brake fluid inspection: Check level and condition every 100 hours.
Valve clearance adjustment: Check every 200 hours.

CAUTION! Use only Yamaha recommended fluids and parts. Incorrect maintenance can lead to component failure.

Specifications

Engine: 400cc, 4-stroke, SOHC, air-cooled single cylinder.
Bore x Stroke: 83.0 mm x 73.0 mm.
Compression Ratio: 8.3:1.
Fuel System: Mikuni BST33 carburetor.
Ignition System: DC-CDI.
Starting System: Electric and auxiliary recoil.
Transmission: Ultramatic automatic V-belt, H/L/N/R/P.
Final Drive: Shaft drive with On-Command 2WD/4WD.
Suspension Travel: Front 6.7 in (170 mm), Rear 7.1 in (180 mm).
Brakes: Hydraulic disc, front dual piston, rear single piston.
Tires: Front AT25 x 8-12, Rear AT25 x 10-12.
Dimensions (LxWxH): 81.5 in x 46.1 in x 47.6 in (2070 x 1170 x 1210 mm).
Dry Weight: 551 lbs (250 kg).

Engine Service

Detailed procedures for engine disassembly, inspection, and reassembly.

Cylinder Head & Valves: Removal, valve clearance adjustment, valve guide and seat inspection.
Cylinder & Piston: Piston ring installation, cylinder inspection, piston pin removal.
Crankcase & Crankshaft: Splitting crankcase, connecting rod inspection, crankshaft bearing replacement.
Lubrication System: Oil pump inspection, oil pressure testing, oil cooler service.
Cooling System: Fan motor testing, thermostat replacement (applicable models).

Chassis & Suspension

Frame, suspension, and steering component service.

Front suspension: Remove wheel, shock absorber, upper and lower arms. Inspect bushings and ball joints.
Rear suspension: IRS removal, shock service, swingarm bearing inspection.
Steering system: Handlebar removal, steering stem bearing adjustment/replacement.
Wheels & Tires: Tire removal/installation, wheel bearing inspection, axle service.

Tip: Use a torque wrench for all critical fasteners. Refer to torque specifications chart.

Electrical System

Battery, charging system, starting system, and lighting.

Battery: Test voltage (12.8V fully charged), clean terminals, check electrolyte level.
Charging system: Test stator resistance (0.1-1.0 Ω), check regulator/rectifier output.
Starting system: Test starter motor draw, inspect starter relay, check solenoid.
Lighting: Test headlight, taillight, brake light bulbs and circuits.
Switches: Test handlebar switches (start, light, 4WD, differential lock).

WARNING! Disconnect battery before testing. Use a multimeter for accurate diagnostics.

Fuel System

Carburetor service, fuel pump, tank, and lines.

Carburetor removal: Drain fuel, disconnect cables and hoses, remove mounting bolts.
Carburetor disassembly: Remove float bowl, jets, needle valve, diaphragm.
Cleaning: Use carburetor cleaner and compressed air on all passages and jets.
Adjustments: Set float height, pilot screw (initial setting: 2 turns out), idle speed.
Fuel tank: Remove, clean, inspect for rust or damage.
Fuel lines: Inspect for cracks or leaks; replace if necessary.

CAUTION! Use new gaskets and O-rings during reassembly. Ensure no debris enters carburetor.

Drive System

Transmission, drive shaft, differential, and 4WD system service.

Ultramatic Transmission: V-belt inspection/replacement, sheave service, clutch inspection.
Drive Shaft: Remove, inspect U-joints and splines for wear.
Front & Rear Differential: Drain fluid, inspect gears and bearings, adjust backlash.
On-Command System: Test 4WD engagement motor, inspect wiring and switches.
Differential Lock: Test actuator, inspect cable and linkage.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, compression	Check fuel flow, spark plug, compression (should be 128 psi min).
Poor performance/loss of power	Clogged air filter, carburetor, exhaust	Clean/replace air filter, clean carburetor jets, check exhaust restriction.
Transmission slipping	Worn V-belt, clutch issues	Inspect V-belt for wear/cracks; check clutch weights and springs.
4WD not engaging	Electrical issue, mechanical fault	Test 4WD switch and motor; inspect differential engagement mechanism.
Electrical failure (no lights/start)	Battery, fuse, wiring	Test battery voltage; check main 30A fuse; inspect for loose/corroded connections.
Overheating	Low oil, clogged cooling fins	Check oil level and condition; clean cylinder head and oil cooler fins.
Excessive vibration	Engine mount, drive shaft, wheels	Inspect engine mounts; check drive shaft U-joints; balance wheels.

Reset: For electronic issues, disconnect battery for 10 minutes to reset ECU.

Service: For technical support, contact Yamaha Motor Corporation at 1-800-962-7926 or visit www.yamahamotorsports.com.

Wiring Diagrams

Complete electrical schematics for the Grizzly 400 are included in the full manual. Diagrams cover main harness, lighting system, starting/charging circuits, and switch connections. Use for tracing wires, identifying connectors, and diagnosing electrical faults.

Note: Always refer to the diagram specific to your model year. Wire colors and connector positions may vary.