Spark
Plugs and What They Say ... |
Look at the spark
plug porcelain for the color and condition of it. Plug colors tell the
mechanic how the engine is running and can be very important. Plugs change
colors and the different colors can explain such things as if the engine
is running too hot or if the engine is worn. The color should be read by
looking at the porcelain insulator and compared to the plugs shown on the
next few slides.
A tan colored plug
means that the engine is running normal and the air/fuel mixture is correct.
This is the correct color a spark plug should be and it tells the mechanic
everything is fine with the engine. The mechanic would install a new properly
gapped plug. When installing a new plug, replace the old one with the same
heat range. The plug below shows normal wear in the center electrode. A
new plug would have square edges that helps the plug fire better.
A black dry fluffy
colored plug is caused by deposits from a carburetor that is running too
rich (too much gas), or excessive idling on some engines. Black smoke coming
from the exhaust is a sign of a rich air/fuel mixture. The rich air/fuel
mixture must be repaired before installing a new spark plug. Common causes
for a rich air/fuel mixture are:
* dirty air filter.
* air mixture screw
or carburetor needs adjusting.
* choke is sticking.
* carburetor float
height is out of adjustment or float is sticking open.
A black wet glazed
colored plug is caused by the burned oil that is leaking past the piston
rings or valve guides and burning in the cylinder. This engine will have
blue smoke coming out of the exhaust. It is a sign that the engine will
need rebuilding. Two strokes that have this color spar plug are burning
the transmission oil from the crankcase. If a new spark plug is installed
it will foul and quit working. Common causes for this problem are:
* Worn piston and
rings.
* Worn cylinder bore.
* Worn valve guides.
* Crankshaft seals
are bad or cases that need lapping (if on a two stroke engine with a transmission).
A white colored
plug is caused by engine overheating. Failure to repair this engine will
result in severe engine damage. Common causes for this are:
* Incorrect spark
plug (too hot heat range).
* Low octane fuel.
* Timing is not set
properly.
* Cooling problems,
(dirty cylinder fins, no or low water if water cooled, low or no engine
oil).
* Carburetor air/fuel
mixture is too lean (too much air).
* Leaking crankshaft
seals, no oil, base or head gasket leaks, or crankcase leaks on two stroke
engines.
The plug below shows
what can happen when something hits the spark plug. Something from inside
the engine has hit the plug and this problem must be repaired before running
the engine further. Make sure the spark plug is the correct length for
the engine.
Excessive detonation
has caused the porcelain on this plug to break away. If this engine is
allowed to run, engine damage can occur. Make sure the fuel octane is high
enough for the engines requirements.
The plug below has
carbon across the plug gap. This is usually caused by carbon that is loosened
and it lodges between the gap causing the plug to misfire.
The plug below was
caused by pre ignition and failure to repair this condition will cause
engine damage. Check for the following:
* correct heat range
plug
* over advanced ignition
timing
* lean air/fuel mixture
* cooling system
* lack of lubrication*
The plug below is
worn out from being used for a long period of time. Notice how the center
electrode is round and worn from use. A spark plug that is worn takes a
lot more voltage to fire and can cause poor engine running.
thanks to
motocross.com
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