Applicable to Carburetted Petrol Engines. In Fuel Injected engines, the fuel/air ratio is constantly monitored and adjusted by the Engine Management System or ECU.
In order to adjust the Fuel/Air ration of any carburetted engine, you need some kind of measuring device. Some okes play it by ear. Some will run the engine for a while and inspect the colour of the plug electrode. This might be effective, but its time consuming. And with the various petrol grades you get these days, it becomes very difficult to do correctly.
Another way to do this, is to use a Gas Analyser. Some has an air tube that you clamp to the exhaust outlet. And it analyses the exhaust gases as you make small adjustments to the Air or Fuel correction screws. Some screw into the spark plug.
Unfortunately, these Analysers are a bit expensive. Fine if you have a Garage and enough work to justify the costs, but not for the ‘once only’ private person. Technological advances has resulted in some of these analysers as small as wrist watches, but if you want something robust and reliable, expect to fork out a lot of money.
Then there is ColourTune. An old but reliable device. Its basically a spark plug, that allows you to see what happens inside the combustion chamber. Very scarce in South Africa and most of the older mechanics used to have them. Nowadays most cars are Fuel Injected and there is no need for such a device, but its ideal for our carburetted scooters.
If you can lay your hands on one of these, consider yourself very lucky. And if you know where one can buy locally, let us know.
Here is a Video of it in action.