Midwest Track & Training Reviews
2026 Yamaha YZ125
Owner’s Spec & Maintenance Reference
125cc 2-stroke
A verified reference compiled by MWR — not a reproduction of the factory manual.
1Full Specifications
| Displacement | 125 cc |
|---|---|
| Bore × stroke | 54 × 54.5 mm |
| Cooling | Not documented |
| Induction | reed-valve inducted |
| Power valve | Not documented |
| Starter | Not documented |
| Transmission | 6-speed |
| Clutch | Not documented |
| Final drive | Chain |
| Front suspension | KYB Speed-Sensitive System inverted fork; fully adjustable |
|---|---|
| Front travel | 11.8 in |
| Rear suspension | KYB single shock; fully adjustable |
| Rear travel | 12.4 in |
| Front brake | 270 mm |
| Rear brake | 240 mm |
| Front tire | 80/100-21 Bridgestone Battlecross X20F |
| Rear tire | 100/90-19 Bridgestone Battlecross X20 |
| Seat height | 38.6 in |
|---|---|
| Wheelbase | 56.9 in |
| Ground clearance | 14.4 in |
| Weight | 212 lb (Wet weight) |
| Fuel capacity | 1.8 gal |
| Fuel / premix | Premix (2-stroke) |
| MSRP (new) | Not documented |
2Fluids & Capacities
Safety-critical — published only from the service/owner’s manual for this exact year-model. Always confirm against your manual before service.
Not documented from the service manual for this year — consult the factory manual.
3Torque Specifications
Safety-critical — listed only as published in the service manual for this exact year-model. Use a calibrated torque wrench.
Not documented from the service manual for this year — consult the factory manual.
4Maintenance Schedule
Guideline intervals — they vary by year and how hard the bike is ridden. Confirm exact figures in your owner’s manual.
| Service item | Interval | Notes |
|---|---|---|
| Air filter — clean or replace | every ride | Do this basically every ride. A clogged filter chokes power; a torn one lets grit into the engine. |
| Transmission oil | ~every 10 h | A two-stroke’s gearbox runs on its own oil — clean trans oil keeps shifting and the clutch crisp. |
| Top-end / piston check | ~every 30 h | 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.) |
| Chain & sprockets | ~every 40 h | A worn chain and sprockets rob power and can snap. Replace as a set. |
| Coolant | ~every 50 h | Fresh coolant stops overheating and corrosion. Roughly once a season for most riders. |
| Grease linkage & bearings | ~every 20 h | Re-greasing the suspension linkage and wheel bearings keeps the bike handling right and saves bearings. |
5Known Issues & Fixes
No verified year-specific issues documented yet.
6Common Upgrades
Not documented yet.
7Owner Tips
Not documented yet.
9Official Manuals
No verified factory manual linked for this year yet — always service to your model-year service manual.