Kohler 3.5CFZ, 4CZ, 5CFZ, 6.5CZ Problem Means of Identification Possible Cause Normal, Oil fouled

Problem	Means of Identification	Possible Cause
Normal	Light tan or gray deposit on the	Good operating conditions and
	firing tip.	maintenance.
Gap bridged	Deposits built-up and closing gap	Oil or carbon fouling. Clean and
	between electrodes.	regap.
Oil fouled	Wet black deposits on the insulator	Excessive oil entering combustion
	shell bore electrode.	chamber through worn rings and
		pistons, excessive clearance
		between valve guides and stems,
		or worn or loose bearings.
		Replace plug.
Carbon fouled	Black, dry fluffy carbon deposits	Using too cold range plug, weak
	on insulator tips, exposed shell	ignition, clogged air intake or
	surfaces, and electrodes.	improper carburetor adjustments,
		defective fuel pump, overrich fuel
		mixture, or excessive no load
		operation. Clean and regap.
Lead fouled	Dark gray, black, yellow, or tan	Caused by highly leaded fuel.
	deposits; or a glazed coating on	Replace plug.
	the insulator tip.
Pre-ignition	Melted electrodes and possibly	Wrong type of fuel, incorrect timing
	blistered insulator. Metallic deposits	or advance, too hot of a plug, burnt
	on insulator suggests internal	valves, or engine overheating.
	engine damage.	Replace and plug.
Overheating	White or light gray insulator with	Engine overheating, wrong type of
	small black or gray/brown spots	fuel, loose spark plugs, too hot a
	with bluish (burnt) appearance on	plug, low fuel pump pressure or
	electrodes.	incorrect ignition timing. Replace
		plug.
Worn	Severely eroded or worn	Caused by normal wear and failure
	electrodes.	to replace at proper interval.
		Replace plug.
	Figure 3-11. Spark Plug Condition

4.Before installing any spark plug, check the gap. See Figure 3-12. The proper gap is attained when the feeler (or wire) gauge just passes between the spark plug electrodes. It should pass easily, but with some resistance or drag. The correct gap is 0.028--0.031 in. (0.7--0.8 mm).

5.To readjust the spark plug gap, use gapping tool to gently bend the side electrode closer to or further from the center electrode. See Figure 3-13. The side electrode must be centered over the center electrode.

6.Being careful not to bump the electrode, hand thread spark plug clockwise into cylinder head until resistance is felt.

7.Using a torque wrench, tighten each spark plug to a torque of 18--22 ft. lbs. (20--30 Nm). If a torque wrench is not available, hand-tighten spark plug until resistance is felt and then use a ratchet wrench to tighten the plug an additional 1/2 turn (if installing a new plug) or 1/8--1/4 turn (if reinstalling a used plug). Do NOT overtighten as this may strip threads or alter electrode gap setting.

8.Check spark plug wire connector in boot for accumulated dirt, grease, etc., and clean as necessary. Firmly push spark plug connector and boot onto spark plug.

3-10 Scheduled Maintenance TP-5695 12/93