I replaced the spark plugs. Before, I used NGK Iridium IX Spark Plugs. (P/N : BPR6EIX)
And currently, I use NGK Iridium MAX Spark Plugs. (P/N : BPR6EIX-P)
Please see below.
![spark plugs](enginroomitems/spark_plugs/001.jpg)
BPR6EIX-P has a long life and the other performance is the same as the BPR6EIX.
Before
![spark plugs](enginroomitems/spark_plugs/002.jpg)
After