Kohler 38RCLA Manual page 59

Problem/Condition Means of Identification
Gap-bridged spark Built-up deposits and gap between electrodes
plug 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 insula-
spark plug tor. Metallic deposits on insulator suggest inter-
nal engine damage.
Overheated spark plug White or light gray insulator with small black or
gray/brown spots with bluish (burned) appear-
ance on electrodes.
Worn spark plug Severely eroded or worn electrodes.
Figure 4-10 Engine Evaluation Using Spark Plug Condition
TP-6810 6/15
Possible Cause/Solution
Oil or carbon fouling. Clean and regap the spark
plug.
Excessive oil entering combustion chamber
through worn rings and pistons, excessive clear-
ance 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 over-
heating. 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 59