Honda’s Kettering ignition is versatile, rugged, simple—and a voltage sponge. Being pretty inefficient with the use of voltage, any small added resistances or imperfect connections tend to disproportionatley weaken it, which is why fifty-year-old electrical connectors are Kettering’s Achilles heel. All in all however it is a remarkably durable and trouble-free ignition. And it was invented four years before the Titanic steamed into the history books! Astonishing, isn’t it?

Kettering has three stages. While the points are closed, current passes from the battery through the key and stop switches, into the ignition coil primary winding, and then back to the battery, creating a magnetic field around that primary winding. When the points open, this current loop is interrupted, making the primary’s magnetic field instantly collapse. This dramatic magnetic activity mutually induces the ignition coil’s secondary winding resulting in a voltage burst to the spark plug, whose current continues to flow through the engine castings and also returns to the battery.

The ignition coil’s two windings are of different gauge wire and different numbers of turns so that the coil steps up the battery’s 12 volts to the 5,000 volts it takes to arc across the spark plug’s gap. For starting and idling, that is. As the bike is ridden—the throttle used, the transmission shifted and various loads encountered—the plug’s voltage requirement goes up and down, and the coil is always ready with the needed voltage, because its capability is designed to be (nominally) 25,000 volts. Interestingly, never is that full amount needed. The coil is simply designed to have the reserve it needs when the spark plug is worn or carboned up.

The Kettering system performs poorly with age and neglect. For example, the plug caps get loose on their wires, resulting in weakened spark and inconsistent engine performance. Honda’s resistive caps also increase resistance with age. Other Kettering faults include ignition coil failure, which happens due to Kettering’s always-on nature overheating its coils. Honda used to sell a great oscillating tool for testing Kettering coils. I rely on it still today, because the official manual’s resistance tests are not to be trusted. It’s also very easy to dynamically test a Kettering coil while it is still on the bike and without special tools. Simply remove the wire at the coil that comes from the points and intermittently ground it (key and kill switches on). Or, if you trust the points and the wire harness, simply wiggle the points with a screwdriver—that’s electrically the same thing. A better test however is to use one of those variable gap testers at the end of the spark plug wire. Or you can make your own out of a spare spark plug, just open the gap to 0.120 inch. Run the engine at various rpm with this tester or homemade tester-plug (it will run on one less cylinder) and watch for a strong, dark blue (bodering on purple) spark with no skips or wavering.

The condensor in a Kettering ignition has one role: to make this collapsing field system’s primary winding’s collapse as sudden as possible. When the points open, the pent-up energy in the coil’s primary wants to partly discharge across the points. If allowed to do so, the primary’s collapse will be damped—i.e. much less immediate, which will lower the induction potential in the coil secondary, greatly reducing plug voltage. The condensor absorbs the rogue spike then feeds that energy back into the coil as the magnetic field wanes. Most four-stroke Hondas will start and run without a condensor, but the constant bleed-off of voltage will limit how high in rpm the engine will rev. Many people opt for electronic ignition either thinking it will improve performance or to eliminate the need for maintenance. The kind of electronic ignition most buy—the simple points replacment type (think Dyna S)—will not increase performance. Other more sophisticated kinds of aftermarket ignitions might, but that’s only in the sense that a significantly modified engine needs that kind of computerized ignition, not because the ignition necessarily brings a performance advantage in and of itself. If your unmodified bike is running properly, you have little to gain; if you have kept up on your bike's maintenance, the benefit of a higher-voltage coil will be so small you may never notice it. Maintain your ignition system and the engine will respond by carbureting its best. Yes, carburetion is improved because the better your ignition system works, the fewer demands are made on the exactness of the air/fuel mixture. Hence, carburetion shines.

Factory Honda points can last 20,000 miles. They have tungsten faces and are constructed in a high quality way as to machining, parts and assembly. Every maintenance service (every 2500-3000 miles for many vintage Hondas) inspect the points’ faces and if rough dress them with a Flexstone, a special points dressing file. After dressing the points wash them well with brake aerosol and after blowing dry, polish them with a business card. The use of non-OEM points is a bad idea. And as with everything else these days, watch out for counterfeit points that are plainly poorly made but have the factory’s TEC, ND, or Hitachi stamping on them.

Timing the Kettering ignition by using a “deadlight” can be very accurate. But you will still want to strobelight-check the full advance. Don’t use a Phillips screwdriver on the Honda points plate screws. The screws may look like Phillips, but they are actually flat-blade. Even then you will want to grind a special flat-blade screwdriver to fit the screws more carefully. Like a lot of things about Hondas, this is taken for granted by career mechanics.

The philosophical and cultural changes of the past fifty to seventy-five years have taken their toll on the otherwise simple task of servicing and tuning the Kettering ignition. It can no longer be assumed that the skill is as easily acquired, and more importantly, that the ethos, the realization, of the adjustment’s importance to overall engine function is as easily accepted by today’s rider as it was fifty years ago. Unfortunately, it definitely is not.