How to use a Colortune

How to use a Colortune

This guide captures ‘bygone’ advice on how to use a Colourtune as part of the mixture setting process on a Classic Car. It is part of a series I am building that describes what to do on a Classic Car Basic Service.

Useful information for Classic Car and Retro Car enthusiasts, as many of these tasks are no longer required on modern day cars.

Remember folks these are ‘bygone guides’ … useful but the safety and personal protective equipment measures are reflective of bygone awareness. Stay safe.





What is a Colortune

A Colortune kit is a simple and accurate means of adjusting carburation. It consists of a glass-topped spark-plug through which the colour of the flame in the combustion chamber can be determined.

The Colortune carburettor adjustment kit in component form
The Colortune carburettor adjustment kit in component form

Basically a rich mixture burns with an orange flame, while a weak mixture is bright blue. The carburettor is adjusted in the normal way until the flame is brilliant blue speckled with orange.

The mixture in some recent carburettors cannot be altered so the flame will always be weak.

Below explains how to set the Colortune up.


How to set up a Colortune

With the engine thoroughly warm, remove No 1 spark-plug and fit the Colortune 500 plug in its place
With the engine thoroughly warm, remove No 1 spark-plug and fit the Colortune 500 plug in its place
Screw the plain end of the black adaptor lead on to the centre electrode of the plug, taking care not to damage the electrode
Screw the plain end of the black adaptor lead on to the centre electrode of the plug, taking care not to damage the electrode
Slide the lower half of the viewerscope over the adaptor lead and pus!J the clawed end over the flats of the hexagonal plug
Slide the lower half of the viewerscope over the adaptor lead and pus!J the clawed end over the flats of the hexagonal plug




Bend the adaptor lead to one side then slide it up the slot in the upper half of  the scope, pushing it onto the lower half
Bend the adaptor lead to one side then slide it up the slot in the upper half of the scope, pushing it onto the lower half
With the viewerscope in position, clip the free end of the adaptor lead into the plug cap. Adjust the viewerscope mirror
With the viewerscope in position, clip the free end of the adaptor lead into the plug cap. Adjust the viewerscope mirror
The viewerscope is included so that any spark-plugs that are awkward to reach can be seen easily. It need not always be used
The viewerscope is included so that any spark-plugs that are awkward to reach can be seen easily. It need not always be used
Start the engine and adjust the tickover to about 800 rpm. On fixed-jet carburettors this ensures the idling jet is operating
Start the engine and adjust the tickover to about 800 rpm. On fixed-jet carburettors this ensures the idling jet is operating
Start the engine and you s. 1ould be able to see the flame colour. Adjust the mixture screw (or jet nut) until the flame is blue
Start the engine and you s. 1ould be able to see the flame colour. Adjust the mixture screw (or jet nut) until the flame is blue
The adaptor lead or viewerscope may be used to remove the hot spark-plug from the engine after loosening with a plug spanner
The adaptor lead or viewerscope may be used to remove the hot spark-plug from the engine after loosening with a plug spanner

Gunson Colortune Kits on eBay


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