I had to pull the headers for some other maintenance, noticed the coloring of the exhaust valves. The picture is #4 and #6 exhaust port but all the exhaust valves have similar appearance. The engine is a carbureted 350 with iron vortec heads, about 20,000 miles since I built it. I always run 91 octane pure gas when I can get it. I'm just curious if this is normal or if there is some problem lurking. I'm not that knowledgeable about this and appreciate comments from those who have the experience.
