Honda EM25 Manuel De L'utilisateur page 43

6.Install the spark plug carefully by hand, to avoid cross-threading.
7.After a new spark plug has been seated by hand, it should be
tightened 1/2 turn with a wrench to compress its washer.
If a used plug is being reinstalled, it should only require 1/8 to 1/4
turn after being seated.
8.Reinstall the spark plug cap on the spark plug securely.
CAUTION:
• The spark plug must be securely tightened. An improperly tightened
plug can become very hot and possibly damage the generator.
• Never use a spark plug with an improper heat range.
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