Motorcycle Owners Club

Honda CG125 but also some universal motorcycle information

Colortune Review

The Colortune device is a spark plug that allows you to see the colour of the flame
inside the combustion chamber (engine) when the petrol ignites.

All you have to do is look at the colour.
Yellow is rich, white is lean, deep blue is perfect (light blue is a little lean).
It really is as simple as that.

Of course you want to see if the flame changes colour at different throttle positions and engine revs,
so you simply turn the throttle on the bike. This is done with the gearbox in neutral so the bike is not moving.

The Colortune device is very useful for finding and fixing faults because it shows you immediately when it is fixed.
If you are a more advanced enthusiast / mechanic,
it can help you get the mixture correct when fitting non-standard exhausts / air filters / carb or engines.

The CG125 engine uses the 12 mm version of the Colortune (make sure you obtain the 12 mm version).
12 mm is a very common size of spark plug used in motorcycles of all engine sizes (including large engines).
So the chances are the Colortune will be with you for a long time
and it's even more useful when working with engines that have more than one cylinder.
All NGK spark plugs that begin with D are 12 mm.

How To Use

1. Warm your bike up to normal temperature, remove your spark plug.

2. Use a dab of grease to hold the copper washer on the Colortune plug.

3. Gently tighten the Colortune plug hand tight just to make a snug seal (a 16 mm deep socket may help, do not use a ratchet).

4. Attach the extension and connect your HT lead (plug cap), make sure your plug cap is out of the way (not touching anything).

5. Start your engine and look at the colour, adjust your Idle Mixture Screw to get correct colour.
(you may find you have to open the throttle very slightly or turn up the Idle speed screw to stop it from stalling)

6. Carbs fitted with accelerator pump
the idea is a yellow colour as throttle is opened and then settles back to blue at a steady throttle opening.
This can be a bit fiddly to get right.

Do not over rev the engine by holding the throttle fully open for too long (only go to full throttle for a fraction of a second).
To prevent excessive heat build-up in the Colortune and engine,
you should not use it continuously for more than 5 minutes and avoid extended high rpm.
When you have finished with the Colortune, the plug will be hot so be careful.

Carburetion Basics
Spark Plug Colour Chart

Some links I have found on the internet about the Colortune

User Manual
(more complicated than it is in reality to use, but also covers the advanced things for real enthusiasts / professionals).


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