The Colortune has a clear spark plug that lets you look into the combustion chamber while the engine is firing. The colour of the combustion flame tells you if the mixture is correct. With the carburettor mixture screw you can then adjust the flame colour to get the correct mixture.
Supplied with a viewerscope for bright light conditions, and viewing in recessed engines
The Colortune is £35. If you buy several products together you will get an offer price.
Also available is the Colortune "A" kit. This is a complete 10mm kit with spare 12mm and 14mm plugs. With these 3 plugs it will fit most any motorcycle. If you work on several bikes this kit is best value at £63. (Bought separately it would cost £71)
See this page for full details and pick the correct size Colortune to fit your vehicle. http://www.carbtune.com/colortune.html