Seven different types of ignition systems have been used on powersports engines in the last roughly hundred years. Two yardsticks offer the best way to compare these seven systems. The first is the ignition system's power source. The source is important because DC-powered ignitions behave one way and AC systems in another way. The other very useful ignition system metric is whether the ignition fires its spark plug by rising its primary winding’s magnetic field or by collapsing it. Rising field systems are more powerful and tend to be more tolerant of spark plug deposits than are collapsing field ignitions. Therefore, all the strengths and weakness, the pros and cons, and even the development histories, of all the ignitions found as original equipment on powersports vehicles, which ultimately reveal their real-world differences, are rooted in these two characteristics, AC or DC powered, and rising or collapsing field. So that's how we'll divide these systems.

Magneto
Standard on nearly every very early motorcycle and car, magneto's main strength was its simplicity. Its greatest weaknesses was its legendary intolerance of dirt and its extreme sensitivity to timing. Because it is AC-powered, the magneto ignition’s source voltage rythymically goes through a zero point, the midpoint in the AC sinewave. Due to either dirt or wear, the points-open timing can happen closer to this zero spot than normal, and the result is vastly reduced voltage and even weak or no spark. In fact, points that are no dirtier than average and would therefore not phase another system just plain knock this one out. And its collapsing field characteristic—the fact that the system goes through two stages before it fires—just further reduces this ignition’s potential. It’s a delicate, somewhat below middle-grade ignition system, despite its endearingly vintage and even (in some circles) tough-guy persona, not to mention the present resurgence of its performance cachet in vintage performance circles. Though magneto virtually defined such machines as the British twins of the 50s and early 60s, today magneto ignition as original equipment is rare and found solely on portable generators, lawn equipment, chainsaws and the like. It gets the job done, but it is the least visible and the least viable system today in the powersports world.

Energy transfer
Energy transfer is probably best known for its appearance on pushrod Triumph twins, but it has also powered many smaller Asian bikes. It's often mistaken for magneto but though similar in some respects it is actually much further developed and better performing. Unlike magneto which is collapsing field, ET is a rising field system wherein the spark fires instantly on coil buildup, making it more effective in the presence of spark plug deposits. You can easily distinguish energy transfer from magneto by counting the windings: two windings make it magneto, three characterize energy transfer. Though a very different system, energy transfer shares magneto’s sensitivity to timing and point cleanliness, which can keep the engine from starting, though that’s not at all hard to fix. In just minutes I have brought kids’ ET ignition equipped Honda Z50s back to life while anxious moms stood gratefully by. No joke.

Capacitor discharge
CDI is unique. It begins with a higher source voltage than any other ignition system, then stores this energy in a capacitor, whose triggered massive burst into the ignition coil makes for a blasting, rising-field effect. With such dramatic spark plug power, CDI easily overcame the early snowmobiler's major problem--his two-stroke engine's spark-plug-trashing oil deposits. CDI is historic on that basis alone, in addition to its famous support of factory roadracers and motocross bikes of all kinds. CDI's one significant weakness however is a spark duration that is inherently one-third that of other ignitions, and this drawback in connection with less than abundantly rich, emissions-spec roadgoing engines has resulted in it not being utilized on street-legal motorcycles as much as it otherwise might have been. Do not confuse, as many do, CDI with so-called “electronic ignition”. CDI is not simply another name for transistorized ignition, despite so much bad misinformation online, especially among people who pretend to know better. Multi-spark versions of CDI have eliminated CDI's characteristic short duration drawback, but CDI developed in this way has not appeared in vehicle production (showing that streetbikes really don't benefit from it) but rather on the aftermarket.

Kettering
Named after its inventor, a GM engineer, and often called "battery/point", Kettering is monumental in its history and longevity. Invented in 1908, its being battery-powered contributes to its classic drawback of being a power hog. As rpm increase, Kettering struggles to keep up and voltage to the ignition coil drops precariously low. Therefore, dirty wiring, corroded connectors or switches, or a less than perfect battery can make Kettering perform below its best. Further, its collapsing field design makes it less tolerant of spark plug deposits than it might otherwise be. However, due to its simplicity and ruggedness, virtually all four-stroke Japanese road bikes on the road today have Kettering ignition, either in its original contact points form or its later transistorized form.

Transistorized Kettering
Often called "electronic" ignition (and each of the Big Five has its own proprietary name--Honda's is "TPI"), in transistorized Kettering the points were replaced with a transistor, which did the switching duty. Also a new part emerged, the electronic trigger, or pulser, which took over the points’ timing job. Other than this, there is absolutely no difference between first-generation transistorized Kettering and traditional points-based Kettering. They differ only in the parts that do the switching and timing. This is also true of aftermarket Kettering systems such as the Dyna S and all of its contemporaries. Therefore, transistorized Kettering, just like standard Kettering, is a voltage-hog. And, advertising notwithstanding, transistorized Kettering—whether OEM or aftermaket—offers no gain in ignition performance over the original Kettering.

Transistorized magneto
As electronics became more widespread, the magneto system lost its points, just as Kettering did. Tansistorized magneto is found mostly on stationary engines such as portable generators, lawn equipment, and a few very early model utility vehicles such as Kawasaki Mules (because they initially had stationary engines as powerplants). Transistorized magneto and traditional magneto differ only in the transistor and trigger replacing the points.

Transistorized energy transfer
Energy transfer also eventually got transistorized. You can now find transistorized energy transfer ignition on smaller-engined powersports products such as utility vehicles, scooters, and smaller offroad vehicles, ones that had standard energy transfer in earlier years. And, just as with the two Ketterings and the two Magnetos, other than the transistor and trigger, energy transfer and transistorized energy transfer are exactly the same system.

These then are the seven ignition systems used as original equipment in powersports vehicles. All are still to be found, and even the most advanced ignitions available today, no matter what they're called or how sophisticated they appear, have one of these systems at their core.