1987 Polaris Trail Boss 250 Service Manual

The 1987 Polaris Trail Boss 250 is a rugged all-terrain vehicle featuring a 244cc air-cooled 2-stroke engine, automatic Polaris Variable Transmission (PVT), front and rear suspension systems, hydraulic disc brakes, and durable chassis design. This service manual provides comprehensive technical information for maintenance, repair, and troubleshooting procedures. Below are key sections covering specifications, maintenance schedules, engine service, transmission, electrical systems, and troubleshooting.

1. Specifications 2. Maintenance Schedule 3. Engine Service 4. Transmission System 5. Electrical System 6. Brake System 7. Suspension & Steering 8. Fuel System 9. Lubrication System 10. Troubleshooting

Specifications

Technical specifications for the 1987 Polaris Trail Boss 250 ATV.

Component	Specification
Engine Type	244cc Air-cooled 2-stroke single cylinder
Bore x Stroke	70mm x 64mm
Compression Ratio	6.5:1
Fuel System	Mikuni VM34SS carburetor
Transmission	Polaris Variable Transmission (PVT)
Drive System	Chain drive with automatic clutch
Front Suspension	Independent double A-arm
Rear Suspension	Swingarm with dual shocks
Front Brakes	Hydraulic disc
Rear Brakes	Hydraulic disc
Fuel Capacity	3.5 gallons (13.2 liters)
Dry Weight	348 lbs (158 kg)

Maintenance Schedule

Recommended maintenance intervals for optimal performance and longevity.

Daily: Check fuel level, tire pressure, brake operation
Every 25 hours: Clean air filter, check spark plug
Every 50 hours: Change engine oil, inspect drive chain
Every 100 hours: Clean carburetor, check valve clearance
Every 200 hours: Replace spark plug, inspect suspension components
Seasonal: Change gear oil, inspect brake pads

WARNING! Always perform maintenance in well-ventilated area. Allow engine to cool before servicing.

Engine Service

Detailed procedures for engine maintenance and repair.

Spark Plug: NGK BR8ES, gap 0.020-0.024 inches
Cylinder Head: Torque to 18 ft-lbs in crisscross pattern
Piston & Rings: Replace if compression below 100 psi
Carburetor Adjustment: Pilot screw 1-1/2 turns out from lightly seated
Ignition Timing: Fixed at 0.118 inches BTDC
Cooling System: Clean cooling fins regularly

CAUTION! Use genuine Polaris parts for optimal performance and reliability.

Transmission System

PVT System: Automatic continuously variable transmission
Drive Belt: Polaris #3211084, inspect for wear and cracking
Clutch: Automatic centrifugal type, service every 100 hours
Chain Drive: #520 chain, adjust tension to 1/2-3/4 inch play
Gear Oil: SAE 80W-90, capacity 12 oz (350ml)
Primary Reduction: 2.353:1 ratio
Secondary Reduction: 3.076:1 ratio

Electrical System

Complete electrical system specifications and service procedures.

Battery: 12V 14Ah, maintain specific gravity 1.265-1.299

Charging System: AC magneto, output 140W at 6000 RPM

Ignition: CDI electronic ignition, spark advance mechanical

Lighting: Headlight 35/35W, taillight 5W, brake light 21W

Fuses: Main 15A, spare fuse included in fuse box

Wiring: Color-coded harness, inspect for chafing and corrosion

Brake System

Hydraulic disc brake maintenance and service procedures.

Front Brakes: Single piston caliper, rotor diameter 7.5 inches
Rear Brakes: Single piston caliper, rotor diameter 7.5 inches
Brake Fluid: DOT 4, change every 2 years or 200 hours
Pad Replacement: Replace when thickness below 1/16 inch
Bleeding Procedure: Use reverse bleeding method for best results

Tip: Always clean brake components with brake cleaner only.

Suspension & Steering

Front and rear suspension system service and adjustment.

Front Suspension: Double A-arm with 5.5 inches travel
Rear Suspension: Swingarm with dual shocks, 5.0 inches travel
Shock Adjustment: Pre-load adjustable via spring collars
Steering Stem: Torque nut to 65 ft-lbs
Wheel Bearings: Grease every 100 hours
Tire Pressure: Front 3.5 psi, Rear 3.5 psi (standard)
Toe Adjustment: 0-1/4 inch toe-out

WARNING! Always support ATV properly when working on suspension components.

Fuel System

Carburetor and fuel delivery system service procedures.

Mikuni VM34SS Carburetor Specifications:

Component	Specification
Main Jet	#180
Pilot Jet	#40
Needle Jet	Q-2
Jet Needle	6DH4-3
Throttle Valve	2.5
Float Level	0.98 inches (25mm)

Lubrication System

Engine oil and lubrication system maintenance.

Oil Type: Polaris 2-stroke injection oil or equivalent

Oil Tank Capacity: 1.5 quarts (1.4 liters)

Oil Pump: Mechanical type, adjustable cable

Mixing Ratio: 40:1 if pre-mix required

Oil Injection Cable: Adjust for proper alignment marks

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, compression	Check fuel flow, spark plug, compression (min 100 psi)
Poor performance	Carburetion, exhaust	Clean carburetor, check exhaust restriction
Transmission slipping	Belt wear, clutch	Inspect drive belt, clean clutch components
Electrical failure	Battery, connections	Test battery voltage, check ground connections
Brake issues	Fluid, pads, air	Bleed brakes, check pad thickness, fluid level
Overheating	Cooling, lubrication	Clean cooling fins, check oil injection system

Technical Support: Contact Polaris customer service for genuine parts and technical assistance.

Parts Information: Use original Polaris part numbers for replacement components.