With NGK spark plugs the lower the number the hotter the heat range . D8HA is the replacement spark plug . If the air/fuel ratio is a little rich or the motor is using a little oil (past the rings or valve guides ) a hotter heat range plug may be suitable . D6HA's fit but may be too hot and not color the porcelin a light tan /brown. If you've run the engine and the plugs are white you need the change plugs to a colder heat range .
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