Honda CBR125RW - Service manual > Troubleshooting

ENGINE DOES NOT START OR IS HARD TO START

1. Spark Plug Inspection

Remove and inspect spark plug.

Is the spark plug in good condition?

NO -

• Incorrect spark plug heat range
• Incorrect spark plug gap
• Dirty air cleaner

YES - GO TO STEP 2.

2. Spark Test

Perform spark test.

Is there good spark?

NO -

• Faulty spark plug
• Loose or disconnected ignition system wires
• Broken or shorted spark plug wire
• Faulty ignition coil
• Faulty CKP sensor
• Faulty ignition switch
• Faulty ECM
• Faulty engine stop switch (CM and U type)

YES - GO TO STEP 3.

3. Fuel Pump Inspection

Check for operation of the fuel pump and inspect the fuel flow.

Is the fuel pump unit normal?

NO - Faulty fuel pump unit

YES - GO TO STEP 4.

4. PGM-FI System Inspection

Check the PGM-FI system.

Is the PGM-FI system normal?

NO - Faulty PGM-FI system

YES - GO TO STEP 5.

5. Cylinder Compression

Test cylinder compression.

Is the compression specified?

YES -

• Valve stuck open
• Worn cylinder and piston rings
• Damaged cylinder head gasket
• Seized valve
• Improper valve timing

NO - GO TO STEP 6.

6. Engine Starting Condition

Start by following normal procedure.

Does the engine start then stops?

YES -

• Faulty IACV
• Leaking insulator or intake manifold
• Improper ignition timing (Faulty ECM or CKP sensor)
• Contaminated fuel

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.

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.

POOR PERFORMANCE AT LOW AND IDLE SPEED

1. Spark Plug Inspection

Remove and inspect the spark plug.

Is the spark plug in good condition?

NO -

• Plug not serviced frequently enough
• Incorrect spark plug heat range
• Incorrect spark plug gap

YES - GO TO STEP 2.

2. Ignition Timing Inspection

Check the ignition timing.

Is the ignition timing as specified?

NO -

• Faulty ECM
• Faulty CKP sensor
• Improper valve timing

YES - GO TO STEP 3.

3. Fuel Pump Inspection

Inspect the fuel flow.

Is the fuel pump unit normal?

NO - Faulty fuel pump unit

YES - GO TO STEP 4.

4. PGM-FI System Inspection

Check the PGM-FI system.

Is the PGM-FI system normal?

NO - Faulty PGM-FI system

YES - GO TO STEP 5.

5. IACV Inspection

Check the IACV operation.

Does the IACV operates normal?

NO - Faulty IACV

YES - GO TO STEP 6.

6. Intake Pipes Leaking Inspection

Check for leaks at the insulator or intake manifold.

Are there leaks?

YES -

• Loose insulator
• Damaged insulator
• Damaged intake manifold

POOR PERFORMANCE AT HIGH SPEED

1. Ignition Timing Inspection

Check the ignition timing.

Is the ignition timing as specified?

NO -

• Faulty ECM
• Faulty CKP sensor
• Improper valve timing

YES - GO TO STEP 2.

2. Fuel Pump Inspection

Inspect the fuel flow.

In the fuel pump unit operation normal?

NO - Faulty fuel pump unit

YES - GO TO STEP 3.

3. PGM-FI System Inspection

Check the PGM-FI system.

Is the PGM-FI system normal?

NO - Faulty PGM-FI system

YES - GO TO STEP 4.

4. Valve Timing Inspection

Check the valve timing.

Is the valve timing correct?

NO - Cam sprocket not installed properly.

YES - GO TO STEP 5.

5. Valve Spring Inspection

Check valve springs.

Is the valve spring free length as specified?

NO - Faulty valve spring

YES - GO TO STEP 6.

6. Camshaft Inspection

Remove and inspect the camshaft.

Is the cam lobe height as specified?

NO - Faulty camshaft

YES - Camshaft is OK.

POOR HANDLING

Steering is heavy

• Steering stem adjusting nut too tight
• Damaged steering head bearings
• Insufficient tire pressure
• Faulty tire

Either wheel is wobbling

• Excessive wheel bearing play
• Bent rim
• Improperly installed wheel hub
• Excessively worn swingarm pivot bushings
• Bent frame

Motorcycle pulled to one side

• Front and rear wheels not aligned
• Bent fork
• Bent swingarm
• Bent axle
• Bent frame

 

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