1986 Honda 250 Engine Manual

The 1986 Honda 250 engine is a reliable 250cc four-stroke powerplant known for its durability and performance in various Honda motorcycles. This manual covers essential information including specifications, maintenance procedures, troubleshooting, and repair guidelines for proper engine care and operation.

1. Engine Specifications 2. Maintenance Schedule 3. Oil Change Procedure 4. Valve Adjustment 5. Carburetor Settings 6. Ignition System 7. Cooling System 8. Engine Disassembly 9. Torque Specifications 10. Troubleshooting Guide

Engine Specifications

Complete technical specifications for the 1986 Honda 250 engine.

Specification	Details
Engine Type	4-stroke, air-cooled, single cylinder
Displacement	249cc
Bore x Stroke	73mm x 59.5mm
Compression Ratio	9.3:1
Carburetor	Keihin 28mm
Ignition System	CDI electronic ignition
Starting System	Electric and kick start
Oil Capacity	1.5 liters with filter change
Recommended Oil	10W-40 motorcycle oil
Fuel Type	Regular unleaded gasoline

Maintenance Schedule

Regular maintenance intervals for optimal engine performance.

Oil Change: Every 3,000 miles or 6 months
Oil Filter: Replace with every oil change
Valve Clearance: Check every 6,000 miles
Spark Plug: Replace every 7,500 miles
Air Filter: Clean every 3,000 miles, replace every 12,000 miles
Coolant: Replace every 2 years or 24,000 miles

WARNING! Always perform maintenance with engine cool and motorcycle on center stand.

Oil Change Procedure

Step-by-step guide for changing engine oil.

Run engine for 5 minutes to warm oil
Place drain pan under engine drain plug
Remove drain plug and allow oil to drain completely
Replace oil filter using proper filter wrench
Reinstall drain plug with new washer (torque: 22 ft-lbs)
Add 1.3 liters of new 10W-40 oil
Start engine and check for leaks
Check oil level and add if necessary

CAUTION! Hot engine oil can cause burns. Wear protective gloves.

Valve Adjustment

Proper valve clearance adjustment procedure.

Intake Valve Clearance: 0.05mm (0.002 in)
Exhaust Valve Clearance: 0.08mm (0.003 in)
Tools Required: Feeler gauge set, socket set, screwdriver
Engine Position: Top dead center on compression stroke

Adjust valves when engine is cold. Rotate engine until timing marks align.

Carburetor Settings

Standard carburetor adjustments and specifications.

Setting	Specification
Main Jet	#115
Pilot Jet	#38
Needle Position	3rd clip from top
Float Height	14.5mm
Idle Speed	1,300 ± 100 RPM
Air Screw	1.5 turns out

Adjust idle mixture screw for smoothest idle after engine warm-up.

Ignition System

Ignition system components and maintenance.

Spark Plug: NGK DR8ES-L, gap 0.7-0.8mm
Ignition Timing: Fixed at 15° BTDC at 1,400 RPM
Pickup Coil Resistance: 50-200 ohms
Ignition Coil Resistance: Primary 0.1-0.3Ω, Secondary 7-12kΩ

Tip: Always check spark plug condition during routine maintenance.

Cooling System

Air cooling system maintenance and care.

Keep cooling fins clean and free of debris
Ensure proper oil level for engine cooling
Check for oil leaks around cylinder head
Maintain proper engine tune to prevent overheating
Use recommended oil viscosity for optimal heat dissipation

WARNING! Never operate engine with blocked cooling fins.

Engine Disassembly

Basic engine disassembly sequence.

Drain engine oil and coolant
Remove carburetor and intake manifold
Disconnect exhaust system
Remove cylinder head cover
Remove camshaft and timing chain
Remove cylinder head
Remove cylinder and piston
Split engine cases if necessary

CAUTION! Mark all components for proper reassembly.

Torque Specifications

Critical torque values for engine components.

Component	Torque Value
Cylinder Head Bolts	20 ft-lbs
Spark Plug	13 ft-lbs
Oil Drain Plug	22 ft-lbs
Oil Filter	12 ft-lbs
Camshaft Sprocket	17 ft-lbs
Clutch Spring Bolts	7 ft-lbs

Always use a calibrated torque wrench for accurate tightening.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Hard starting	Dirty carburetor, weak spark	Clean carburetor, check spark plug and ignition
Poor performance	Clogged air filter, incorrect timing	Replace air filter, check ignition timing
Overheating	Low oil, lean mixture	Check oil level, adjust carburetor mixture
Excessive oil consumption	Worn piston rings, valve seals	Compression test, inspect valve seals
Engine knocking	Low oil pressure, worn bearings	Check oil pressure, inspect crankshaft bearings

Service Note: Always diagnose systematically from simplest to most complex issues.

Technical Support: Contact authorized Honda service center for complex repairs.