Yamaha YZF-R125 Service Manual: Poor medium-and-high-speed performance

Incorrect engine idling speed

Engine 1. Cylinder and cylinder head Incorrect valve clearance Damaged valve train components 2. Air filter Clogged air filter element Fuel system 1. Throttle body Damaged or loo ...

Shift pedal does not move

Shift shaft Improperly adjusted shift rod Bent shift shaft Shift drum and shift forks Foreign object in a shift drum groove Seized shift fork Bent shift fork guide bar Transmission ...

Other materials:

Assembling the oil pump
1. Lubricate: Oil pump inner rotor Oil pump outer rotor Oil pump driven gear (with the recommended lubricant) 2. Install: Oil pump outer rotor Oil pump inner rotor "1" Oil pump driven gear Pin "2" NOTE: When installing the inner rotor, align the pin "2" in the oil pump sh ...

Starting the engine
In order for the ignition circuit cut-off system to enable starting, one of the following conditions must be met: The transmission is in the neutral position. The transmission is in gear with the clutch lever pulled and the sidestand up. 1. Turn the key to "ON" and make sure ...

Replacing the air filter element and cleaning the check hose
The air filter element should be replaced at the intervals specified in the periodic maintenance and lubrication chart. Have a Yamaha dealer replace the air filter element more frequently if you are riding in unusually wet or dusty areas. In addition, the air filter check hose must be ...