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BBT-JD420
Spark Plug Service
Recommended spark plugs: BPR6ES (NGK), W20EPR-U (DENSO)
An incorrect spark plug can cause engine damage.
1. Disconnect the spark plug cap, and remove any dirt from
around the spark plug area.
2. Remove the spark plug with a 13/16-inch spark plug
wrench.
3. Inspect the spark plug. Replace it if the electrodes are
worn or heavy carbon build-up is found, or if the insulator
is cracked or chipped.
4. Measure the spark plug electrode gap with a suitable
gauge. The gap should be 0.028-0.031 in (0.70-0.80 mm).
Correct the gap, if necessary, by carefully bending the
side electrode.
5. Install the spark plug carefully, by hand, to avoid cross-
threading.
6. After the spark plug seats, tighten with a 13/16-inch
spark plug wrench to compress the sealing washer.
If reinstalling the used spark plug, tighten 1/8—1/4 turn
after the spark plug seats.
If installing a new spark plug, tighten 1/2 turn after the
spark plug seats.
A loose spark plug can overheat and damage the engine.
Over tightening the spark plug can damage the threads in the cylinder head.
7. Attach the spark plug cap.
Idle Speed Adjustment
1. Start the engine outdoors, and allow it to warm up to operating temperature.
2. Move the throttle lever to its slowest position.
3. Turn the throttle stop screw to obtain the standard idle speed.
Standard idle speed: 1,400 ± 150 rpm
SERVICE & MAINTENANCE
Spark plug
Wrench
Sealing
Washer
Throttle stop screw
0.028-0.031 in
(0.70-0.80 mm)
