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Gunson’s colortune – Supplied by Powerspark Ignition Ltd

Take the guesswork out of engine tuning with Gunson’s colortune, the world famous glass topped spark plug that gives you a window into the combustion chamber so you can see the flame. Why is this important? The flame’s color tells you the richness of the air fuel mixture. A yellow flame means a rich mixture and a blueish white flame a weaker mixture. A Bunsen blue flame is spot on. colortune is so damn simple that anyone can use it. Colortune is unaffected by ambient weather conditions because it works on the law of physics that gases burn with a certain color. Remember high school chemistry lab and the Bunsen burner. So stop reading plugs and start tuning by color.

Use Colortune when you have multiple carbs and don’t want to drill ports in exhaust manifolds and you have a clear line of sight to the top of the spark plug. In a multiple carb application you must be able to associate an exhaust stream with a carb so you can adjust each carb’s fuel mixture by measuring the carb’s exhaust stream. If you just want to set the fuel mixture to it’s correct strength without knowing what that strength is then use colortune.

Information: The correctly proportioned mixture is – 14.7 parts of air by weight to 1 part of fuel.

If there is perfect combustion, all the fuel will be burnt to produce carbon dioxide and water with no carbon monoxide or unburned fuel (hydrocarbons).

The carbon in the fuel burns with oxygen in the air to produce carbon monoxide (CO), which then burns with more oxygen to produce carbon dioxide (CO2).

Hydrogen in the fuel burns with the oxygen in the air to produce water (H2O) Nitrogen in the air passes through to the exhaust with little reaction.

When there is less air in the mixture, there is not enough oxygen to complete the burning process so some carbon monoxide is not changed to carbon dioxide and hydrocarbons (unburned fuel) may be present in the exhaust.

Carbon particles glow yellow in the combustion of a rich mixture and in severe cases you may see black carbon smoke in the exhaust.

When there is too much air in the mixture, it becomes more difficult to ignite, burns slower, and is therefore less efficient. The diluted mixture burns with a pale flame. Misfiring may occur and hydrocarbon levels in the exhaust gas will rise.

Carbon monoxide levels stay low because there is plenty of oxygen available to convert it to carbon dioxide.

Please Download this PDF file for the Colourtune Fuel System Fault Diagnostic Chart it has some really helpful tips to curing problems with Fuel/Air mixture

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