Choosing The Right Spark Plugs For Your Custom
Think of spark plugs as windows into the combustion process. The end of the porcelain closest to the center electrode is used to read the idle mixture. The center portion of the porcelain will indicate part-throttle air/fuel (A/F) mixtures, while the bottom of the porcelain will indicate the wide-open-throttle (WOT) air/fuel ratio. Obviously, a black, sooty plug is way rich and a bone-white porcelain is probably way lean. The best way to judge WOT mixtures is to run the engine at WOT and then cut the ignition clean at the end of the track and safely shift into Neutral. Coast to a safe stop on the return road, pull a spark plug out, and use the viewer to closely inspect the plug.