Yamaha YP125R Service Manual

TROUBLESHOOTING
9-3
Chassis
1. Brake(s)
• Dragging brake
Electrical system
1. Spark plug
• Incorrect spark plug gap
• Incorrect spark plug heat range
2. Ignition system
• Faulty ECU
EAS28610
OVERCOOLING
Cooling system
1. Thermostat
• Thermostat stays open
EAS28620
POOR BRAKING PERFORMANCE
• Worn brake pad
• Worn brake disc
• Air in hydraulic brake system
• Leaking brake fluid
• Faulty brake caliper kit
• Faulty brake caliper seal
• Loose union bolt
• Damaged brake hose
• Oil or grease on the brake disc
• Oil or grease on the brake pad
• Incorrect brake fluid level
EAS28660
FAULTY FRONT FORK LEGS
Leaking oil
• Bent, damaged or rusty inner tube
• Cracked or damaged outer tube
• Improperly installed oil seal
• Damaged oil seal lip
• Incorrect oil level (high)
• Loose damper rod bolt
• Damaged damper rod bolt copper washer
• Cracked or damaged front fork cap O-ring
Malfunction
• Bent or damaged inner tube
• Bent or damaged outer tube
• Damaged fork spring
• Worn or damaged outer tube bushing
• Bent or damaged damper rod
• Incorrect oil viscosity
• Incorrect oil level
EAS28670
UNSTABLE HANDLING
1. Handlebar
• Bent or improperly installed handlebar
2. Steering head components
• Improperly installed lower handlebar holder
• Improperly installed lower bracket
(improperly tightened ring nut)
• Bent steering stem
• Damaged ball bearing or bearing race
3. Front fork leg(s)
• Uneven oil levels (both front fork legs)
• Unevenly tensioned fork spring (both front
fork legs)
• Broken fork spring
• Bent or damaged inner tube
• Bent or damaged outer tube
4. Swingarm
• Worn bearing or bushing
• Bent or damaged swingarm
5. Rear shock absorber assembly(-ies)
• Faulty rear shock absorber spring
• Leaking oil
6. Tire(s)
• Uneven tire pressures (front and rear)
• Incorrect tire pressure
• Uneven tire wear
7. Wheel(s)
• Incorrect wheel balance
• Deformed cast wheel
• Damaged wheel bearing
• Bent or loose wheel axle
• Excessive wheel runout
8. Frame
• Bent frame
• Damaged steering head pipe
• Improperly installed bearing race
EAS28710
FAULTY LIGHTING OR SIGNALING SYSTEM
Headlight does not come on
• Wrong headlight bulb
• Too many electrical accessories
• Hard charging
• Incorrect connection
• Improperly grounded circuit
• Poor contacts (main switch)
• Burnt-out headlight bulb
Headlight bulb burnt out
• Wrong headlight bulb
• Faulty battery
• Faulty rectifier/regulator

Yamaha YP125R Specifications

General

Engine Type	Liquid-cooled, 4-stroke, SOHC, 4-valve
Bore x Stroke	52.4 mm x 57.9 mm
Fuel System	Fuel Injection
Ignition System	TCI
Transmission	V-Belt Automatic
Front Suspension	Telescopic fork
Rear Suspension	Unit Swing
Front Brake	Hydraulic single disc, Ø267 mm
Starter System	Electric
Rear Tyre	140/70-14M/C 62P (Tubeless)