Yamaha YZ450F Owner's Service Manual page 81

TROUBLESHOOTING
The following guide for troubleshooting does not cover all the possible causes of problems. If the following problems occur,
perform the specified checks or maintenance jobs. If a problem occurs that is not listed in this manual or if the problem
cannot be corrected by the procedures provided in this manual, contact your Yamaha dealer.
Engine starting problems, engine idling speed problems, and medium and high-speed performance problems
• Engine does not start even though the kickstarter is pushed.
• Engine starts, but soon stops.
Engine idling speed problems
• Engine idling speed fluctuates.
• Engine idling speed is high.
• Engine idling speed is low.
Medium and high-speed performance problems
• Engine speed does not increase.
• Engine knocks.
• Engine speed increases suddenly.
• Loss of engine power.
INSPECTION STEPS
If the aforementioned problems have occurred, perform the following inspection steps in the order given.
Check that the fuel tank is filled with fresh gaso-
line.
OK ↓
Check that the fuel tank breather hose is not
clogged. (Refer to "INCLUDED PARTS" section
in the CHAPTER 1.)
OK ↓
Adjusting the engine idling speed(Refer to "AD-
JUSTING THE ENGINE IDLLING SPEED" sec-
tion in the CHAPTER 3.)
OK ↓
Check that the fuel hose is connected properly
and is not kinked or pinched.
OK ↓
Check the spark plug for dirt, the spark plug gap,
and the spark plug cap. (Refer to "CHECKING
THE SPARK PLUG" section in the CHAPTER 3.)
OK ↓
Check that the air filter element is installed cor-
rectly and is not clogged. (Refer to "CLEANING
THE AIR FILTER" section in the CHAPTER 3.)
OK ↓
Checking the sensors, injector and ignition coil
connection.
OK ↓
Installed condition of ECU (Refer to "CHECKING
THE ECU" section in the CHAPTER 7.)
OK ↓
Check the assembled condition of the throttle
body, and check the throttle valve and its sur-
rounding parts for dirt.
OK ↓
Consult a Yamaha dealer.
No good →
Fill the fuel tank.
No good →
Repair or replace.
No good →
Adjust.
No good →
Repair.
No good →
Clean or adjust.
No good →
Clean or repair.
No good →
Repair or replace.
No good →
Repair.
No good →
Repair or clean.
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ELECTRICAL