Yamaha YZF-R125 Service Manual: Unstable handling

Handlebars

- Bent or improperly installed right handlebar

- Bent or improperly installed left handlebar

1. Steering head components

- Improperly installed upper bracket

- Improperly installed lower bracket (improperly tightened ring nut)

- Bent steering stem

- Damaged ball bearing or bearing race

2. 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

3. Swingarm

- Worn bearing

- Bent or damaged swingarm

Rear shock absorber assembly

- Faulty rear shock absorber spring

- Leaking oil

Tire(s)

- Uneven tire pressures (front and rear)

- Incorrect tire pressure

- Uneven tire wear

Wheel(s)

- Incorrect wheel balance

- Deformed cast wheel

- Damaged wheel bearing

- Bent or loose wheel axle

- Excessive wheel runout

Frame

- Bent frame

- Damaged steering head pipe

- Improperly installed bearing race

    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 assembly bo ...

    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 or light switch) - ...

    Other materials:

    Checking the shift drum assembly
    1. Check: Shift drum groove Damage/scratches/wear Replace the shift drum assembly. Shift drum segment "1" Damage/wear  Replace the shift drum assembly. Shift drum bearing "2" Damage/pitting Replace the shift drum assembly. ...

    Checking the cylinder and piston
    1. Check: Piston wall Cylinder wall Vertical scratches Replace the cylinder, and replace the piston and piston rings as a set. 2. Measure: Piston-to-cylinder clearance a. Measure cylinder bore "C" with the cylinder bore gauge. NOTE: Measure cylinder bore "C" by takin ...

    Checking the cylinder head
    1. Eliminate: Combustion chamber carbon deposits (with a rounded scraper) NOTE: Do not use a sharp instrument to avoid damaging or scratching: Spark plug bore threads Valve seats 2. Check: Cylinder head Damage/scratches   Replace. Cylinder head water jacket Min ...

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