Spark Plug

Yamaha Engineers choose Genuine Yamaha spark plugs carefully during the design process to provide high performance, consistent ignition spark and long service life.
A large number of modern motorcycles, scooters and ATV's use computer controlled electronic fuel injection and ignition timing systems, so careful attention is paid to matching the spark plug to these electronic control systems.

The Feature of Parts

  • Spark Plugs Selected to Match Engine Characteristics
  • Durability and Reliability for Consistent High Quality Ignition Spark under High-pressure and High-temperature Conditions

Maintenance

Periodic Inspections & Maintenance

Worn or damaged spark plugs can cause hard starting and decrease engine power. Spark plugs should be regularly inspected and replaced when necessary and following the Scheduled Maintenance chart in the Owner's or Service Manual.

Inspecting Spark Plugs for Discoloration

Spark plugs should be regularly inspected and replaced when necessary and following the Scheduled Maintenance chart in the Owner's or Service Manual.
When there the condition of the plugs is abnormal, replace them even if the regular replacement period has not elapsed. If there are significant differences in the condition of the cylinders, the unit should be checked by a Yamaha dealer.

Inspection of the Spark Gap

Check the spark gap using the Owner's or Service Manual. The correct spark gap is vital to the overall performance of the engine.
Special care needs to be used when checking 'fine wire' electrode spark plugs.
Special tools are required to measure the spark gap, it is recommended this inspection be performed by a Yamaha dealer.

Table of Items to Regularly Inspect

Refer to the applicable service manual for the inspection and maintenance procedures.

General Periodic Maintenance
ITEM ROUTINE INITIAL ODOMETER READINGS ANNUAL CHECK
1000km
(600mi)
10000km
(6000mi)
20000km
(12000mi)
30000km
(18000mi)
40000km
(24000mi)
Spark plugs Check condition.        
Adjust gap and clean.
Replace.      
*Since these items require special tools, data and technical skills, have a Yamaha dealer perform the service.

Problems and Counter-measures

Carbon Accumulation (fouling)

This refers to the electrodes and insulator being covered with carbon. Carbon is an electrical conductor which can cause ignition misfire.
Fouling can cause starting problems, as well as performance problems during operation.
Possible causes include extending operation of the engine at very low temperatures, an overly rich running engine - too much gasoline (incorrect carburetor setting, or some failure), or not enough intake air (clogged air filter or restricted intake system).
Other causes can include ignition timing too far retarded, and using a colder heat range spark plug than is specified for the model.
Carbon fouled spark plugs should NOT be cleaned, and the unit should be inspected by a Yamaha dealer to determine the cause for the fouling.

Overheating

This state occurs when the electrodes are worn by the heat and can no longer fire normally. Overheating can cause a loss of power when driving at high speed or with a heavy load.
Possible causes include improperly tightened spark plugs, engine cooling problems, pre-ignition, a spark plug heat rating which is too low, and severe abnormalities in combustion.
Severe engine damage can occur from continued operation with any of the above conditions. The unit should be inspected by a Yamaha dealer as soon as possible.

Knocking

This is abnormal combustion which occurs when the temperature and/or pressure of the combustion chamber are too high, and the air-fuel mixture ignites before the ignition spark occurs. Problems such as a loss in power and engine damage can result.
Possible causes include advanced ignition timing, too lean air-fuel, or using gasoline with too low octane value.

Severe engine damage can occur from continued operation with any of the above conditions. The unit should be inspected by a Yamaha dealer as soon as possible.

Pre-ignition

When the air-fuel mixture ignites and begins to burn before the ignition spark occurs is referred to as Pre-Ignition. It is sometimes a result of overheated spark plug electrodes.
Pre-ignition can cause melting or burnout of the center electrode and/or outer electrode of the spark plug. Problems such as a loss in power and engine damage can result.
Possible causes include a hotter heat range spark plug than is specified, advanced ignition timing, incorrect fuel settings and cooling system problems.
Severe engine damage can occur from continued operation with any of the above conditions. The unit should be inspected by a Yamaha dealer as soon as possible.

Flash-over

Flash-over is where the high voltage from the ignition system discharges, or 'jumps', from the spark plug terminal to the metal shell.
The sparking over the surface of the insulator may melt the seal of the spark plug cap.
It may be caused by wear in the electrodes widening the spark gap which increases the required voltage to jump between the electrodes, causing spark leakage at the insulator. Another possible cause is deterioration, or damage to the spark plug cap which allows moisture to enter.
If the spark gap is the problem, replace the spark plugs with new ones. If the spark plug caps are the problem, replace them with new ones.


Frequently Asked Questions

[Questions About Spark Plugs and Their Performance]

Q1: Is it OK to use a spark plug with a different heat range than originally were installed?

A1: It is very rare to need a different heat range spark plug.
If the spark plugs are fouled, due to operation in certain conditions, a hotter heat range spark plug could be installed, BUT, only after the unit has been closely inspected to make sure some type of failure is not causing the spark plug fouling.
And, if the spark plugs appear to be overheating in certain conditions, a colder heat range plug could be installed, BUT again, only after the unit has been closely inspected to make sure some type of failure is not causing the overheating.
Installing spark plugs of the wrong heat range could result in severe engine damage.

Q2: What are the symptoms of wear in the spark plugs?

A2: Engine starting may become more difficult and engine power may decrease. Hard starting may also be caused by a low battery. The cause of a decrease in engine power is usually something other than spark plugs.
The most important thing is to inspect the spark plugs regularly and replace them as needed or following the Scheduled Maintenance chart.
Hard starting and performance problems can be difficult to diagnose, customers should rely on their Yamaha dealer to determine the cause for these problems.

[Questions About Maintenance]

Q3: Can spark plugs be replaced easily?

A3: Access to the spark plugs varies a great deal depending on the model.
Customer should be informed to first install plugs by hand and then using a spark-plug wrench or socket, properly torque the plugs to the specification in the Owner's or Service Manual.
Be careful to not allow the spark-plug wrench or socket to be at an angle when tightening a spark plug - the tool might contact and break the ceramic insulator portion.
Also, be careful not to 'cross-thread' the spark plug, most cylinder heads are aluminum which is easily damaged by the steel spark plug threads.

Q4: I have screwed the spark plug in off-center (commonly known as 'cross-threaded') and damaged the threads in the cylinder head - What should I do?

A4: The unit should be checked and repaired by a Yamaha dealer. If the threads in the cylinder head are damaged, combustion gas may leak. If the threads cannot be repaired, it will be necessary to replace the cylinder head.

Q5: In a multi-cylinder engine, is it necessary to replace all the spark plugs at once?

A5: Generally, all the spark plugs should be replaced at the same time. If the condition of the spark plugs differ greatly between cylinders, the unit should be inspected by a Yamaha dealer.
Make sure to install spark plugs with the correct heat range.

Q6: What does the color of the insulator indicate?

A6: Inspecting the color of the insulator is commonly called 'reading' the spark plug.
Generally spark plugs from a good running engine, in good condition, will range from medium to light brown (carbureted engines) to very light tan to almost no color (electronic controlled fuel injected models).
But the color will also depend on the amount of usage, it takes a little time for plugs to start to show some color.

Very dark to black appearing plugs usually indicate a fouled spark plug.
A flat black appearance is usually from a overly rich running engine - such as too much gasoline (incorrect carburetor setting, or some failure), or not enough intake air (clogged air filter or restricted intake system).

A shiny black appearance can be caused by too much motor oil in the combustion chamber - such as worn engine components or seals, overfilled crankcase, etc.

The unit should be inspected by a Yamaha dealer to determine the cause.

A spark plug that shows no color and signs of being extremely hot - severely eroded electrodes, and blisters or other damage to the insulator - indicate Overheating.
This can be caused by a lean condition in the fuel system, a problem in the cooling system, ignition timing too far advanced, and other reasons as well. Severe engine damage can occur from continued operation with any of the above conditions. The unit should be inspected by a Yamaha dealer as soon as possible.