Article on The Internet Mini Encyclopædia
Colourtune - what is it?
"It's a special spark plug with a transparent/translucent insulator. It lets you see the colour of the burn. The colour depends on the mixture, and is quite visible at night. A very simple, clever gadget that can have a fair bit to say about what's going on inside. Not sure about the price, I bought mine about a decade and a half ago.
"Any decent parts/accessory/home mechanic store should have one or know about them and be able to get one in. Shouldn't be expensive. [In Australia] try a Repco or East Coast Spares, or in Melbourne I know Ryan's have them."
Ed: in the UK, Gunson's colourtunes are available in stores such as Halfords, for somewhere in the region of 20 UKP. In my limited expereience I've not had much luck with mine, but having said that there's other stuff wrong with the engine let alone the state of tune ;-)
Colourtune - what is it? #2
"The Colourtune is a quartz window spark plug that lets you see into the combustion chamber when the car is idling. You peer into the window whilst the engine is idling.
"After several years of dyno tuning British cars with a four gas exhaust analyzer, I still found the Coloutune to be an invaluable tuning aid.
"On an A series engine the inner cylinders run different air fuel mixtures than the outer cylindrers, so your air fuel mixture is a compromise. I found that the engines usually ran best when the leanest cylinders were on the verge of running blue and the richer cylinders were very yellow with the engine fully warm.
"It is easy to spot a misfiring cylinder because it shows no combustion flame. If you keep richening the mixture and the cylinders still runs blue, then you may have a vacuum leak. You can diagnose many problems that occur at idle, or high speed idle at say, 3000 rpm.
"The Colourtunes do not work to diagnose problems that occur while the engine is under load, most notably because you have to be running alongside the car peering into the little window, but also because there is considerable risk that the quartz window material could blow out into your face because of the high combustion pressures. That safety note being said, I did run several cars on my dyno with the Colourtune installed, and I am still alive to talk about it. I also inhaled carbon monoxide fumes for eight years while tuning cars so my judgement may be suspect...
"If you are thinking ahead of the game you may realize that you could save time buying four Colourtunes as you could adjust the mixture whilst looking at all four cylinders at the same time. Naturally I also tried this because I could write all four off my taxes. The engine will not run right with so many Colourtunes installed. Some engines ran okay with two installed at the same time, but four was too many, even for an eight cylinder Aston Martin.
"Save your money and just buy one for your Mini :)"
UPDATED 16 DEC 2002
Join the Minilist share your joys and woes with 500+ mini owners worldwide via Minilist at Yahoogroups
07 May 2003