[G.M.]

I'm with Jerry. As cheap as GOOD NGK plugs are and as long as they last I never DEEP clean them. Once in a while if I have them out I clean the ends with a small wire brush and rince them out with carb cleaner. However it is good to test them on a tester that has adjustable air pressure to simulate fireing under compression. Some plugs will fire and look good up to 25 lbs of compressed air but above that the compression blows the spark out. G.M.