6-3
SERVICE
SPARK PLUG SERVICE
Spark plugs should be removed, inspected and adjusted
periodically. Replace the spark plugs every 100 hours or
annually.
Check the air gap(s) with a spark plug gap gauge and
adjust accordingly. Set the spark plug gap at .030" (.762
mm). (Illust. 6-5)
6-5
CONDITIONS CAUSING FREQUENT
SPARK PLUG FOULING
1. Air cleaner is restricted. (Replace)
2. Partially closed choke shutter. (Check operation)
3. Poor grade of gasoline. (87 octane minimum)
4. Improper fuel. (Old, stale or mixed)
5. Restricted exhaust system. (Remove and inspect
muffler for restrictions or loose baffles)
6. Incorrect spark plugs. (Check reach and number)
7. Incorrect spark plug gap. (Adjust gap)
8. Oil level is too high, or the breather is restricted.
9. Worn piston rings.
10. Weak ignition system. (Air gap to wide, partially
grounding wires or faulty safety switches)
IGNITION TIMING
In order for an engine to run efficiently, the spark must
ignite the compressed air-fuel mixture when the piston
is in a specific position to deliver maximum power. This
position is known as Before Top Dead Center (BTDC). If
the mixture is ignited too soon, kickback can be
experienced due to pre-ignition. If the mixture is ignited
too late, loss of power can be experienced due to retarded
spark. A partially sheared or the wrong flywheel key can
cause kickback, loss of power, or an inability to start the
engine. Check the flywheel key if one of these symptoms
exist. See Chapter 7 under “Service” for the disassembly
procedure.
Replace the plug if the points on the base of the plug are
pitted or burned, or if the porcelain is cracked anywhere.
When reinstalling the plug make sure it is clean and free
of all foreign material.
NOTE: NEVER use a sand blaster to clean plugs,
microscopic particles left in the plug can score the engine
cylinder during operation. Use a solvent and a wire brush
to clean. Using eye protection, blow out thoroughly with
compressed air.
Replace the spark plug with the proper spark plug.
Consult the parts breakdown for the spark plug to be
used in the engine being serviced.
Install the spark plug, being careful not to cross thread.
Tighten the spark plug to 21 foot pounds (28 Nm) of
torque. If a torque wrench is not available, turn the spark
plug in as far as possible by hand, then use a spark plug
wrench to turn the plug 1/2 turn further. If installing a
used plug, only 1/8 to ¼ turn after seat is needed.
GAP GAUGE
.030”
(.762 mm)
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