Blue spark plug wires12/9/2023 ![]() Also of note is this answer on the physics stack exchange which says that the blue color of air sparks comes from ionization of nitrogen atoms. I don't have the background to tell who's right and was wondering if someone more knowledgeable could give me some verification here.Īs a side note 7/16th is about 1.1cm, and the breakdown voltage for air at sea level is about 30kv/cm. An air/gas mixture at high pressure creates a much denser gap for the spark to jump then in out in the open. Most manuals will give an air gap recommendation for a spark test. The gap is determined by the amount of voltage generated by the ignition, spark plug gap, and the compression ratio. My experience has shown a strong blue spark with a noticeable popping noise in a healthy ignition. You can then also increase engine rpm to verify spark at higher speeds. This means that the spark must jump the 7/16" gap and the spark plug gap in the motor while running. I use mine in line between the spark plug installed normally in the engine and the plug wire. The recommended 7/16" gap has always worked for me on outboard motors. Here's another guy saying basically the same thing: But on an automotive engine with a higher compresssion ratio and under transient conditions the yellow spark can get quenched thereby causing a misfire. 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. Where with most air cooled small engines they operate under a static condition or a steady state.Ĭompression ratio of an engine and the amount of fuel being delivered can have an effect on how well the spark plug fires. An automobile engine operates under a transient condition where the RMP's change so fuel demand changes. That's because the compression ratio is higher than that on an air cooled small engine. On an automobile ignition system the spark should be bright blue. This poster on another site responding to a similar question about the above Briggs and Stratton quote says: I might note though that the very fast, very high voltage sparks in todays systems usually are not blue. Here's another person saying spark color doesn't matter: However, they are talking about small air cooled engines, and are using a specific Briggs and Stratton spark tester with a fixed gap for small air cooled engines, the 19368 model. Orange and yellow come from particles of sodium in the air ionizing in the high energy of the spark gap. ![]() Blue spark is cold in comparison to ultra-violet. The hottest spark is ultraviolet which we can't see. Spark color determines virtually nothing. A yellow/orange spark signifies weak ignition. For example, this Brigg's and Stratton site says:Ī bright blue spark is best. I ask because I've seen conflicting opinions on this matter. If I'm using a spark tester with an adjustable gap set to the correct gap for my car's ignition system voltage, what should the spark look like?
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