The 1986 Yamaha YZ250 is a legendary motocross bike featuring a 249cc two-stroke liquid-cooled engine, 43mm conventional forks, Monoshock rear suspension, and distinctive yellow and black racing livery. This manual covers maintenance, specifications, troubleshooting, and operational procedures for this classic motocross machine. Below are key sections for safety, features, maintenance, specifications, operation, and troubleshooting.
Key components: 249cc two-stroke engine, Monoshock rear suspension, 43mm conventional forks, digital CDI ignition, aluminum swingarm.
| Feature | Description |
|---|---|
| Engine Type | 249cc liquid-cooled two-stroke single |
| Bore x Stroke | 68.0mm x 68.6mm |
| Compression Ratio | 8.5:1 |
| Carburetor | Mikuni VM38SS |
| Ignition | CDI digital |
| Transmission | 5-speed constant mesh |
| Front Suspension | 43mm conventional telescopic forks |
| Rear Suspension | Monoshock with adjustable preload |
| Front Brake | Single disc 240mm |
| Rear Brake | Single disc 220mm |
Always wear proper safety gear and inspect bike before riding.
WARNING! This is a high-performance racing motorcycle. Proper training and experience required. Never operate under influence of drugs or alcohol.
Regular maintenance ensures optimal performance and longevity.
| Service | Frequency |
|---|---|
| Engine oil change | Every 15 hours or 3 races |
| Air filter cleaning | Every ride in dusty conditions |
| Spark plug replacement | Every 25 hours |
| Chain adjustment | Every ride |
| Fork oil change | Every 40 hours |
| Brake fluid change | Every 30 hours |
| Wheel bearing inspection | Every 50 hours |
| Suspension service | Every 60 hours |
Familiarize yourself with all controls before operation.
Left Handlebar: Clutch lever, horn button, choke knob.
Right Handlebar: Front brake lever, throttle, kill switch, start button.
Operation: Start with choke on cold engine. Allow warm-up before riding. Use proper shifting technique - do not force gears.
CAUTION! Always use proper riding technique. This bike has significant power and requires experienced handling.
Two-stroke engine requires specific maintenance procedures.
WARNING! Always use proper fuel mixture. Incorrect mixture can cause engine seizure.
Proper suspension setup is crucial for handling and control.
Tip: Adjust suspension for rider weight and riding conditions.
CDI ignition system provides reliable spark.
CAUTION! Keep electrical components dry and clean.
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| Hard starting | Fouled plug, stale fuel | Replace spark plug, drain old fuel |
| Poor performance | Clogged air filter, jetting | Clean air filter, check carburetor jets |
| Overheating | Low coolant, lean mixture | Check coolant level, richen mixture |
| Transmission issues | Worn clutch, low oil | Check clutch plates, change transmission oil |
| Brake problems | Worn pads, air in lines | Replace pads, bleed brakes |
Service: Contact authorized Yamaha dealer for major repairs.
Proper storage prevents damage during extended periods of non-use.
CAUTION! Always use fuel stabilizer if storing with fuel in tank.