The spark plug is one of the engine components that can be analysed to gather information about engine carburetion. In fact, carburetion (i.e. the process that regulates the contribution of the mix between mixture and air in the combustion chamber of 2-stroke kart engines, editor's note) has a direct effect on the spark plug, "colouring" its surfaces. Consequently, the analysis of the latter can give fundamental information to understand whether carburetion has been done in a workmanlike manner, or if it needs further adjustments. In fact, carburetion is a fundamental check to avoid causing damage to the engine and to ensure that the potential of the engine is exploited to the maximum. For example, carburetion that is too rich (with an excess of mixture in the air/fuel mix) "throttles" the engine and makes it less incisive, while carburetion that is too lean (with a lack of mixture in the air/fuel mix), prevents correct lubrication and, in addition to causing a drop in performance, it risks causing breakage. It is therefore useful to check the spark plug when in doubt about carburetion, but it is advisable to assess it constantly, ideally at the end of each track session. What is advantageous is that removing the spark plug cap and then unscrewing the component from its housing is an extremely simple and quick activity, unlike what happens when you wish to assess carburetion on a piston crown, using the appropriate torches ( or flexible endoscopes) or by dismantling the canister.
A visual analysis is sufficient to assess the carburetion from a spark plug. Looking at the part of the spark plug that is inserted into the engine, the outer ring indicates the carburetion trend at low engine speeds, in the range from zero to nine thousand rpm. On the other hand, the ceramic centre shows the carburation at high revs, when the engine works above nine thousand rpm. Mainly, there are two aspects to consider when carrying out an assessment: the colour and the possible presence of residues of unburned oil.