On an automobile ignition system the spark should be bright blue. That’s because the compression ratio is higher than that on an air cooled small engine. An automobile engine operates under a transient condition where the RMP’s change so fuel demand changes. Where with most air cooled small engines they operate under a static condition or a steady state.
Compression ratio of an engine and the amount of fuel being delivered can have an effect on how well the spark plug fires. This is called quenching the spark. A low compression engine running at a steady state with a constant fuel supply won’t quench even a spark plug with a yellow spark. But on an automotive engine with a higher compresssion ratio and under transient conditions the yellow spark can get quenched thereby causing a misfire.
This is why if you raise the compression ratio and the amount of fuel being delivered of an automobile engine it can get to the point where the stock coil can’t fire the spark plugs because the spark is being quenched. So you have to step up to a higher output coil such as a MSD or Mallory to overcome the quenching effect. This is why top fuel dragsters don’t use regular coils. Because the engine compression is so high and the amount of fuel being delivered is so much, magnetos are used to overcome the quenching effect on the spark plugs
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