The Colortune allows you to watch the flame in the combustion chamber as adjustments are made. It takes the guesswork out of engine tuning. How does this work? The flame\'s colour tells you the richness of the air/fuel ratio. A yellow flame means a rich mixture and a blueish white flame a weaker mixture. Usually a bunsen blue flame is spot on. The Colortune for Motorcycles and other high performance engines is designed to take the higher heat and pressure of a performance engine; this low volume colortune maintains the compression ratio of the engine, ensuring better firing of the mixture. Colortune for motorcycles lets you look into each cylinder when the engine is running. No more flat spots. Other Size of Gunson Motorcycle Colortune Kit is: 12 mm.