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Motorcycle Sparkplug Maintenance Tips to keep your
motorcycle at peak condition.
Sparkplugs. They do more and can tell you more than you might
Typical Motorcycle Sparkplug
Motorcycle Sparkplug Maintenance
Tip: Correctly reading a spark plug can save you a lot of time
You may of noticed that there are hundreds of types, sizes and
brands of spark plugs on the market. But out of that huge selection,
only a handful will work with the motorcycle engine you own. Also
different brands (NGK, Bosch, DENSO, Champion, Esc) will work better
on different types of engines.
As a general rule of thumb, use the sparkplug your manufacturer
recommends for your motorcycle (same brand and part number).
Unfortunately some spark plugs are very specific to a type of engine
and make only for that engine such as the NGK ME8 for $34.23 per
sparkplug, compared to the "normal" price of $2-4 per sparkplug.
Reading a spark plug correctly: (clickable chart)
There are two different main ways to read a spark plug. #1. The
first way is to just unscrew it out of the engine and take a look at
the end of it, matching the chart below. #2. The second way is the
same as #1 except you go for a really hard high revving ride on the
bike, pull over and then unscrew each plug to read them. (Just make
sure to use gloves as they will be very hot).
A spark plug can easily and quickly tell you the condition of an
engine (good or poor), how it is running (rich or lean) and how much
it will cost to fix it.
Symptoms: Dry sooty deposits indicate a rich mixture or weak
ignition. Causes misfiring, hard shifting and hesitation.
Recommendations: Check for a clogged air element, high float
level, sticky choke and worn ignition points. Use a spark plug with
a longer core nose for greater anti-fouling protection.
Symptoms: Oily coating caused by poor oil control. Oil is leaking
past worn valve guides or piston rings into the combustion chamber.
Causes hard starting, misfiring and hesitation.
Recommendations: Correct the mechanical condition with necessary
repairs and install new plugs.
Symptoms: Blistered, white insulator, eroded electrode and
absence of deposits. Results in shortened plug life.
Recommendations: Check for the correct plug heat range,
over-advanced ignition timing, lean fuel mixture, intake manifold
vacuum leaks and sticking valves. Check the coolant level and make
sure the radiator is not clogged.
Symptoms: Melted electrodes. Insulators are white, but may be
dirty due to misfiring of flying debris in the combustion chamber.
Can lead to engine damage.
Recommendation: Check for the correct plug heat range,
over-advanced ignition timing, lean fuel mixture, clogged cooling
system and lack of lubrication.
HIGH SPEED GLAZING
Symptoms: Insulator has yellowish, glazed appearance. Indicate
that combustion chamber temperatures have risen suddenly during hard
acceleration. Normal deposits melt to form a conductive coating.
Causes misfiring at high speeds.
Recommendation: Install new plugs. Consider using a colder plug
if driving habits warrant.
Symptoms: Combustion deposits lodge between the electrodes. Heavy
deposits accumulate and bridge the electrode gap. The plug ceases to
fire… resulting in a dead cylinder.
Recommendation: Locate the faulty plug and remove the deposits
from between the electrodes.
Symptoms: Brown to grayish-tan color and slight electrode wear.
Correct heat range for engine and operating conditions.
Recommendations: When new spark plugs are installed replace with
plugs of the same heat range.
Symptoms: Light brown deposits encrusted on the side or center
electrodes or both. Derived from oil and/or fuel additives.
Excessive amounts may mask the spark, causing misfiring and
hesitation during acceleration.
Recommendation: If excessive deposits accumulate over a short
time or low mileage, install new valve guide seals to prevent
seepage or oil into the combustion chambers. Also try changing
Symptoms: Rounded electrodes with a small amount of deposits on
the firing end. Normal color. Causes hard starting in damp or cold
weather and poor fuel economy.
Recommendation: Replace with new plugs of the same heat range.
Symptoms: Insulators may be cracked or chipped, improper gap
setting techniques can also result in a fractured insulator tip. Can
lead to piston damage.
Recommendation: Make sure the fuel antiknock values meet engine
requirements. Use care when setting the gaps on new plugs. Avoid
lugging the engine.
Symptoms: After long periods of misfiring, deposits can loosen
when normal combustion temperature is restored by an overdue
tune-up. At high speeds, deposits flake off the piston and are
thrown against the hot insulator, causing misfiring.
Recommendations: Replace the plugs with new ones or clean and
reinstall the originals.
Symptoms: May be caused by a foreign object in the combustion
chamber or the piston striking an incorrect reach (too long) plug.
Causes a dead cylinder and could result in piston damage.
Recommendation: remove the foreign object from the engine and/or
install the correct reach plug.
Tip: Don't use decorative or spark arching type sparkplugs.
There are many different styles and types of sparkplug caps. Try
to use the sparkplug cap that best matches the angle between the
spark plug wire and spark plug itself. No matter what shape the
spark plug cap is, is will perform the same.
Try to avoid "decorate" or spark arching type spark plug caps as
they will LOWER the power to the sparkplug and you will have a
weaker spark on stock systems.
Types of Motorcycle Spark Plug Caps
Tip: If you use the exact same sparkplug as your motorcycle
manufacturer recommends the sparkplug should be (99%) properly
gapped to the correct size. Checking a gap only takes seconds to do.
Always check that the spark plug gap is compatible
with the engine manufacturers specification. A gap that is too small
means that the spark duration will be very quick and the spark will
be thin and weak. The consequences of this may be bad starting and
high exhaust emission levels. This will result in an increase in
fuel consumption. If the gap is set too large, the ignition system
will not be able to cope with the demands and a misfire situation
will occur. Some wide gap spark plugs have a longer ground electrode
to accommodate a wide gap setting. These must be used where
specified, as opening up a standard plug to a wider gap setting may
result in the electrodes not running parallel to each other. This
could result in abnormal and premature electrode wear.
Hot and Cold Sparkplugs
Tip: It is better to fix the problem than to change the
sparkplug to patch it up.
Why Hot and Cold Sparkplugs? Using a hotter or colder sparkplug
can be just the fix to an engine problem. Very basely, if your
motorcycle engine is running hot then try using a colder plug, if it
is running hot try a colder plug.
NGK diagram showing insulator and heat range
- has a longer insulator nose length
- less heat is absorbed by the plug and transferred to the cooling
- the plug runs at a higher temperature
- the plug is more prone to pre-ignition (if greater than 850
- NGK BP5ES is hotter than a BP7ES plug.
- An overheated plug will be white with brown spots.
- has a shorter insulator nose length
- more heat is absorbed by the plug and transferred to the cooling
- the plug runs at a lower temperature
- the plug is more prone to fouling (if less than 500 degrees C)
- NGK BP7ES is cooler than a BP5ES plug.
- A fouled plug will be black and sooty.
Influences to spark plug temperature
Any of the following situations can increase spark plug temperature:
-Lean air/fuel mixtures
-Forced induction (Supercharging, turbocharging or Nitrous)
-Advancing ignition timing
-Higher engine speed
-Higher engine load
-Lower air temperature (more dense air resulting in leaner air/fuel
-Lower humidity (more dense air resulting in leaner air/fuel