Understanding the principle by which COLORTUNE works helps in getting the best out of it. That principle is commonly seen in action or paraffin heaters, gas cookers, or anywhere where a fuel is burnt in air to produce heat or energy. Combustion at its most efficient produces a clear blue flame, various other colors result from inefficient mixtures. Inside an internal combustion engine those same colored flames are present though not normally seen. With COLORTUNE fitted, in place of a sparking plug, the flame is visible through the glass insulator and the fuel is ignited by a spark in the COLORTUNE. This allows the user to obtain greatest engine efficiency by assessing the color and appearance of the flame and correcting any faults thus revealed. Using the product could hardly be easier, fit it into a warm engine, in place of a spark plug, and you are ready to begin. COLORTUNE gives you a fascinating insight to the working of an engine without the usual complexities of most other diagnostic equipment. It can provide a unique view of the behavior of the fuel system in the individual cylinders, which no other equipment can do, saving in many cases time, expense and a great deal of effort in fault diagnosis. A gas analyzer gives an average reading of all cylinders, and no diagnosis of faults or setting errors which affect mixture distribution.

While working with this product be aware that:

  • This product may be used at a wide range of engine speeds but should not be used in an engine under load as overheating and product failure could occur. Take additional care when using the product on an air cooled engine which has no fan assisted cooling. On these engines limit the total test duration to 5 minutes and avoid extended running a high rpm.
  • The viewerscope supplied with this product is made from a glass reinforced heat resistant material but will be damaged by excessive heat before the Colortune plug. If this is damaged it serves as a clear warning of overheating. Obtain a replacement and take more care to avoid overheating. Discontinue use if the product plating is discolored by heat or the glass/ceramic shows signs of damage.

4a - Combustion flame appearance: The general appearance of the combustion flame when viewed through COLORTUNE is as follows:

  • Yellow - Indicates a fuel/air mixture which have excessive petrol content (rich). Like a candle flame; producing more light but less heat.
  • Bunsen Blue - Indicates a mixture which is correctly proportioned.
  • Whitish Blue - Indicates a mixture which has less petrol content (lean). NOTE: this color is more easily seen at higher speeds.

    At idle, engine instability and misfiring may occur before this weak mixture and pale shade of blue is fully visible. There are sometimes exceptions to the above as petrol engines are imperfect machines, these will be described later.

4b - The Science

  • The correctly proportioned mixture is: 14.7 parts of air by weight to 1 part of petrol (hydrocarbon fuel).
  • If there is perfect combustion, all the fuel will be burnt to produce carbon dioxide and water with no carbon Monoxide or unburnt 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 (H20)
  • 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 (unburnt 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.

4c - The Practical details

  • On an engine with one carburettor/single point injection, a single Colortune plug will enable the mixture to be Observed in any cylinder for a quick check, or one cylinder at a time for a more thorough evaluation of a multi-cylinder engine.
  • Twin or multiple fuel systems can even be checked in this way (one cylinder at a time) but it is time consuming and a comparison between cylinders at any instant is not possible.
  • Multi-cylinder engines, particularly those with twin or multiple fuel systems are best tested with a Colortune in each cylinder.
  • Variations in mixture between the cylinders are easier to see and faults can be more easily spotted and rectified.
  • Nowhere is this better demonstrated than on high performance motorcycles - where accurate calibration of at least eight settings on four individual carburettors is a highly skilled task, done mainly by ear.
  • A more accurate setting can be achieved with Colortune in half the time normally taken.

NOTE: A multi-cylinder engine with a carburettor (or injector) to each cylinder and a single exhaust system can not beThoroughly tested with a gas analyzer at the tailpipe. The analyzer only gives an average fuel mixture indication for allCylinders and no warning of large mixture variations due to setting errors or indication of other faults.

  • Modern engines with multipoint injection systems, and earlier high performance car engines with twin or multiple Carburettors, have a lot in common with the example of the motorcycle given previously.
  • Colortune gives a marvelous insight to the inner workings of all these engines, so that errors and faults can be easily spotted. Despite its simplicity, Colortune is an invaluable piece of equipment for the amateur or the Experienced technician.