ENGINE LACKS POWER. Honda CBR125R

The Honda CBR125R is a lightweight and powerful motorcycle designed for both beginners and experienced riders. It features a liquid-cooled, single-cylinder engine with PGM-FI fuel injection, delivering reliable performance. The CBR125R also boasts a modern design with sleek bodywork and a comfortable riding position. This manual provides comprehensive service procedures, maintenance schedules, and troubleshooting information for the CBR125R, ensuring optimal performance and safety.

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TROUBLESHOOTING

ENGINE LACKS POWER

1. Drive Train Inspection

Raise wheel off the ground and spin it by hand.

Does the wheel spin freely?

NO – • Brake dragging

• Worn or damaged wheel bearings

• Bent axle

YES –

GO TO STEP 2.

2. Tire Pressure Inspection

Check tire pressure.

Are the tire pressures low?

YES – • Faulty tire valve

• Punctured tire

NO –

GO TO STEP 3.

3. Clutch Inspection

Accelerate rapidly, shift from first to second.

Does the engine speed change accordingly when the gearshift pedal is applied?

NO – • Clutch slipping

• Worn clutch discs/plates

• Warped clutch discs/plates

• Weak clutch spring

• Sticking clutch lifter mechanism

• Additive in engine oil

• Incorrect clutch lever adjustment

YES –

GO TO STEP 4.

4. Engine Performance Inspection

Accelerate lightly.

Does the engine speed increase?

NO – • Dirty air cleaner

• Restricted fuel flow

• Clogged exhaust system.

YES –

GO TO STEP 5.

5. Spark Plug Inspection

Remove and inspect spark plug.

Is the spark plug fouled or discolored?

NO – • Plugs not serviced frequently enough

• Incorrect spark plug heat range

• Incorrect spark plug gap

YES –

GO TO STEP 6.

6. Engine Oil Inspection

Check oil level and condition.

Is there correct level and good condition?

NO – • Oil level too high

• Oil level too low

• Contaminated oil

YES –

GO TO STEP 7.

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TROUBLESHOOTING

7. Ignition Timing Inspection

Check ignition timing.

Is the ignition timing correct?

NO – • Faulty ECM

• Faulty CKP sensor

YES –

GO TO STEP 8.

8. Cylinder compression Inspection

Test the cylinder compression.

Is the compression as specified?

NO – • Improper valve clearance

• Valve stuck open

• Worn cylinder and piston rings

• Damaged cylinder head gasket

• Improper valve timing

YES –

GO TO STEP 9.

9. Fuel Pump Inspection

Inspect the fuel flow.

Is the fuel pump unit normal?

NO – Faulty fuel pump unit

YES –

GO TO STEP 10.

10. PGM-FI system Inspection

Check the PGM-FI system.

Is the PGM-FI system normal?

NO – Faulty PGM-FI system

YES –

GO TO STEP 11.

11. Lubrication Inspection

Remove cylinder head cover and inspect lubrication.

Is the valve train lubricated properly?

NO – • Clogged oil passage

• Faulty oil pump

• Oil strainer screen not serviced frequently enough

YES –

GO TO STEP 12.

12. Over Heating Inspection

Check for engine over heating.

Is the engine over heating?

YES – • Excessive carbon build-up in combustion chamber

• Use of poor quality fuel

• Wrong type of fuel.

• Clutch slipping

NO –

GO TO STEP 13.

13. Engine Knocking Inspection

Accelerate or run at high speed.

Is there knocking?

YES – • Worn piston and cylinder

• Wrong type of fuel

• Excessive carbon build-up in combustion chamber

• Ignition timing too advance (Faulty ECM or CKP sensor)

NO – Engine does not knock.

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Key features

Liquid-cooled engine
PGM-FI fuel injection
Sleek design
Lightweight
Powerful
Comfortable riding position
Comprehensive service manual

Frequently asked questions

Honda recommends using "4-stroke motorcycle oil" or an equivalent with API classification SG or higher and JASO T 903 standard: MA. The viscosity should be SAE 10W-30.

The recommended cold tire pressure is 200 kPa (2.00 kgf/cm2, 29 psi) for standard riding and 225 kPa (2.25 kgf/cm2, 33 psi) when carrying cargo.

The recommended brake fluid is DOT 3 or DOT 4.

User questions

Jennifer P.

Where is the CKP sensor located?

The CKP sensor's location can be found in the PGM-FI system diagram.

Robert Y.

What is the specified torque for the gearshift return spring pin?

The gearshift return spring pin requires a torque of 25 N·m (2.5 kgf·m, 18 lbf·ft).

Robert Y.

What is the torque specification for the gearshift return spring pin?

The gearshift return spring pin uses 25 N·m (2.5 kgf·m, 18 lbf·ft) of torque.

James G.

Where can I find information about part 10 of the right crankcase cover?

Information about part 10 of the right crankcase cover could not be found in the viewed document. However, the manual references the right crankcase cover in the following sections:

Page 1-16: in the Lubrication & Seal Points section, it mentions the clutch lifter arm hole inner surface (right crankcase cover).
Page 3-14: in the Engine Oil Strainer Screen Removal/Installation section, it refers to removing and installing the right crankcase cover.
Page 4-4: in the Oil Pump Removal section, it says to "Remove the right crankcase cover".

James K.

How to check the coolant level in a CBR125R?

To check the coolant level, examine the reserve tank with the engine at normal operating temperature. The level should be between the 'UPPER' and 'LOWER' lines when the motorcycle is upright. Add recommended coolant to the 'UPPER' line if needed.

James K.

What type of coolant to use for a CBR125R?

Use a high-quality ethylene glycol antifreeze containing silicate-free corrosion inhibitors. For CM type models only, Pro Honda HP coolant or equivalent is recommended.

James K.

How to add coolant to a CBR125R?

Remove the single seat, then the reserve tank cap. Add a 1:1 mixture of distilled water and antifreeze until the coolant reaches the 'UPPER' level line. Reinstall the reserve tank cap and the single seat.