Engine & specifications
- Displacement
- 125cc
- Bore × stroke
- 54 × 54.5 mm
- Cooling
- Not yet documented
- Induction
- reed-valve inducted
- Power valve
- Not yet documented
- Starter
- Not yet documented
- MSRP (new)
- Not yet documented
Transmission
- Gears
- 6-speed
- Clutch
- Not yet documented
- Final drive
- Chain
Suspension
- Front
- KYB Speed-Sensitive System inverted fork; fully adjustable, 11.8-in travel
- Front travel
- 11.8 in
- Rear
- KYB single shock; fully adjustable, 12.4-in travel
- Rear travel
- 12.4 in
Brakes
- Front
- 270mm
- Rear
- 240mm
- Type
- Not yet documented
Wheels & tires
- Front rim
- Not yet documented
- Rear rim
- Not yet documented
- Front tire
- 80/100-21 Dunlop Geomax MX33F
- Rear tire
- 110/100-18 Dunlop Geomax MX33
Dimensions & fuel
- Seat height
- 38.2 in
- Wheelbase
- 57.3 in
- Ground clearance
- 14 in
- Weight
- 212 lb (Wet weight*** includes the vehicle with all standard equipment and all fluids, including oil, coolant (as applicable) and a full tank of fuel. It does not include the weight of options or accessories.)
- Fuel
- 1.8 gal
- Premix ratio
- Not yet documented
Fluids
Not yet documented from the service manual for this year.
Fluid types and capacities vary by year and model — we publish them only from the service/owner's manual. Always confirm against your manual before service.
Torque & spec reference
Not yet documented from the service manual for this year.
Torque values can strip threads or fail a component if wrong — we list them only as published in the service manual for this exact year-model. When in doubt, use your manual and a calibrated torque wrench.
Known issues
No verified year-specific issues documented yet.
Common upgrades
Not yet documented.
Parts compatibility
Not yet documented.
Manual links
We haven’t linked a verified manual for this year yet. Always service to your model-year owner’s/service manual.
Owner tips
Not yet documented.
Maintenance checklist
Do this basically every ride. A clogged filter chokes power; a torn one lets grit into the engine.
A two-stroke’s gearbox runs on its own oil — clean trans oil keeps shifting and the clutch crisp.
The piston and rings wear out. Replacing on time prevents a far more expensive bottom-end failure. (2-strokes need it much sooner than 4-strokes — check your manual.)
A worn chain and sprockets rob power and can snap. Replace as a set.
Fresh coolant stops overheating and corrosion. Roughly once a season for most riders.
Re-greasing the suspension linkage and wheel bearings keeps the bike handling right and saves bearings.
Guideline intervals only — they vary by year and how hard the bike is ridden. Always confirm exact figures in your owner's manual.
Aftermarket parts
Each link opens an Amazon search for this model. MWR earns a small commission at no extra cost to you.
Used buying guide
Not yet documented.
Sources
- Yamaha 2025 YZ125X specs — verified 2026-06-20
Blank fields are values we haven’t verified for this exact year-model yet — we leave them blank rather than guess. Torque and fluid specs are published only from the service manual. Always follow your owner’s manual for service.