Kohler 30RCL Operation page 61

Problem/Condition Means of Identification
Gap-bridged spark Built-up deposits and gap between
plug electrodes closing.
Oil-fouled spark plug Wet, black deposits on the insulator shell,
bore, and electrodes.
Carbon-fouled spark Black, dry, fluffy carbon deposits on insulator
plug tips, exposed shell surfaces and electrodes.
Lead-fouled spark plug Dark gray, black, yellow, or tan deposits; or a
glazed coating on the insulator tip.
Pre-ignition damaged Melted electrodes and possibly blistered
spark plug insulator. Metallic deposits on insulator
suggest internal engine damage.
Overheated spark plug White or light gray insulator with small black
or gray/brown spots with bluish (burned)
appearance on electrodes.
Worn spark plug Severely eroded or worn electrodes.
Figure 4-10 Engine Evaluation Using Spark Plug Condition
TP-6905 7/18
Possible Cause/Solution
Oil or carbon fouling. Clean and regap the spark
plug.
Excessive oil entering combustion chamber through
worn rings and pistons, excessive clearance
between valve guides and stems, or worn or loose
bearings. Replace the spark plug.
Incorrect spark plug, weak ignition, clogged air
intake, overrich fuel mixture, or excessive no-load
operation. Clean and regap the spark plug.
Caused by highly leaded fuel. Replace the spark
plug.
Wrong type of fuel, incorrect timing or advance, too
hot a plug, burned valves, or engine overheating.
Replace the spark plug.
Engine overheating, wrong type of fuel, loose spark
plugs, too hot a plug, low fuel pressure or incorrect
ignition timing. Replace the spark plug.
Caused by normal wear and failure to replace spark
plug at prescribed interval. Replace the spark plug.
Section 4 Scheduled Maintenance 61