Troubleshooting; General Information; Starting Failures; Incorrect Engine Idling Speed - Yamaha FZ 25 2021 Supplementary Service Manual

TROUBLESHOOTING

EAS28450
TROUBLESHOOTING
EAS28460

GENERAL INFORMATION

The following guide for troubleshooting does not
cover all the possible causes of trouble. It should
be helpful, however, as a guide to basic trouble-
shooting. Refer to the relative procedure in this
manual for checks, adjustments, and replace-
ment of parts.
EAS28470

STARTING FAILURES

Engine
1. Cylinder and cylinder head
• Loose spark plug
• Loose cylinder head or cylinder
• Damaged cylinder head gasket
• Damaged cylinder gasket
• Worn or damaged cylinder
• Incorrect valve clearance
• Improperly sealed valve
• Incorrect valve-to-valve-seat contact
• Incorrect valve timing
• Faulty valve spring
• Seized valve
2. Piston and piston ring(s)
• Improperly installed piston ring
• Damaged, worn or fatigued piston ring
• Seized piston ring
• Seized or damaged piston
3. Air filter
• Improperly installed air filter
• Clogged air filter element
4. Crankcase and crankshaft
• Improperly assembled crankcase
• Seized crankshaft
Fuel system
1. Fuel tank
• Empty fuel tank
• Deteriorated or contaminated fuel
• Clogged fuel tank cap breather hole
• Clogged or damaged fuel hose
2. Fuel pump
• Faulty fuel pump
• Clogged fuel pump filter
3. Throttle body
• Deteriorated or contaminated fuel
• Sucked-in air
4. Canister
• Hose clogged
• Hose band / twisted
TROUBLESHOOTING
Electrical system
1. Battery
• Discharged battery
• Faulty battery
2. Fuse(s)
• Blown, damaged or incorrect fuse
• Improperly installed fuse
3. Spark plug
• Incorrect spark plug gap
• Incorrect spark plug heat range
• Fouled spark plug
• Worn or damaged electrode
• Worn or damaged insulator
• Faulty spark plug cap
4. Ignition coil
• Cracked or broken ignition coil body
• Broken or shorted primary or secondary coils
• Faulty spark plug lead
5. Ignition system
• Faulty ECU
• Faulty crankshaft position sensor
• Broken AC magneto rotor woodruff key
6. Switches and wiring
• Faulty main switch
• Faulty engine stop switch
• Broken or shorted wiring
• Faulty neutral switch
• Faulty front, rear or both brake light switches
• Faulty start switch
• Faulty sidestand switch
• Faulty clutch switch
• Improperly grounded circuit
• Loose connections
7. Starting system
• Faulty starter motor
• Faulty starter relay
• Faulty starter clutch
EAS28490

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 loose throttle body joint
• Improperly adjusted engine idling speed (idle
adjusting screw)
• Improper throttle cable free play
• Flooded throttle body
• Faulty air induction system
7-1
TRBL
SHTG