There is much that is misunderstood about motorcycle ignition coils. Seems like the Internet engenders one-dimensional thinking. You know, focusing on one thing to the detriment of several other more important things. For example, all the fuss about engine oil brand and weight when the real, critical issues of JASO and maintaining oil level are ignored. Or fuel's ethanol content when a dozen other aspects of gasoline are far more important and of more practical concern. We're all like 10 year olds with no attention span, latching onto only that thing that looms large, captive to the powersports media's amusement-park-like abandonment to the sensational. 1

In the same way, I sigh inwardly each time someone refers to a coil's primary resistance. You should know that no career tech measures primary resistance. It's not on his radar. It is immaterial. A coil is not properly tested that way, for one thing, and despite all the buzz about it, primary resistance is far from the most important aspect of an ignition coil.

Limiting ourselves to just the conventional ignition coils and not Nology coils or car coils or CDI system coils, the coil aftermarket communicates about their products in terms of three different primary resistances: 2-ohm, 3-ohm and 5-ohm. Let's take these in reverse order. The 5-ohm ignition coils are what many vintage points ignition Hondas (CB550, CB750) came with. The 3-ohm coils coincide with later electronic ignition Hondas (CB900). And the 2-ohm coils represent the historic, earliest available motorcycle high performance coils, usually reserved in the literature for points bikes. What is missed in the discussion of coil primary resistances is the fact that any of these three coils can be used in any of the three target bikes with no ill consequence. Mix 'em up, it just doesn't matter. The theory is that higher resistance primaries are to protect the electronic ignitions, and conversely that lower resistance is for points bikes. However, the stock 5-ohm coils on 70s SOHC fours belies this. Similarly, the 2-ohm coils are said to be incompatible with these same electronic ignitions, yet many have fitted them to OEM electronic ignition equipped DOHC fours with no ill results. An ignition coil's primary resistance plainly isn't as important as many think. 2

It is hopefully not a secret that the reason for the different primary resistances in high performance coils is that originally, during the points era, high performance parts companies made only the lower resistance variety, because all that existed were points bikes and points accept higher than stock current levels that the hi-po coils' lower resistance generates with surprising grace. Doesn't phase 'em. The reason the aftermarket coils were lower resistance than stock was that a high performance ignition coil is one with a higher primary to secondary winding turns ratio. It's cheaper and easier to reduce the primary winding count than to increase the secondary, naturally. Then when electronic ignition emerged in the 1980s, high performance coil manufacturers felt they had to hedge their bets and protect these new electronics by leaving the primaries alone and increasing the secondary winding counts instead to get those higher-than-stock turn ratios. Thus the different resistances.

Much of this I have already written about, but here is one important fact. If your bike is running properly, you have little to gain by going to a high performance ignition coil. Yes, you can widen your plug gap and yes, this has the potential to improve combustion. But the real-world result, especially if you have kept up on your bike's maintenance, is so small you may never notice it. The folks that do notice it are those whose bikes suffer from any one of several tuning deficiencies, and fixing those is what should be done instead and which would net the same result. In a way the high performance ignition coil market, while not causing indifference to proper maintenance, surely has promoted it, "enabling" it as it were, and that is too bad. Misunderstanding prevails. Let's exhaust all the nuances of the stock tuning before we gravitate to modifications that merely cover up our own negligence. 3

If you do get a noticeable benefit from high output coils -- and you very well might -- do you know what really has happened? Where the benefit comes from? Carburetion. What? Yes. While obviously not literally affecting the carburetors, the effect of better ignition causes fueling to be less critical. Makes carburetion shine. Less than perfect carburetion suddenly is super carburetion. Back to that 60/40 rule I have dealt with in other articles. Ignition and carburetion are symbiotic. When either is weak, they both appear weak. Conversely, when one is strong, they both appear strong. Better spark compensates for imperfect carburetion. And visa-versa: exquisitely dialed-in carburetion makes ignition's role easier. This is why a thorough engine tune has such great benefit. It is also why all modern bikes now have really wimpy, coil-over-plug ignition coils. You think those coils are stronger than the old type, or even as strong? They're not. They are far lower voltage and get by with that because of their bikes' fuel injection. Fuel injection's superior atomization makes ignition's job much easier. That 60/40 rule again.

One more thing. Focus on the practical. If a points bike, spend 90 percent of your resourses of both time and money on getting the proper superior-quality OEM points assemblies in there, and time them right, and carefully. Check for cracks in the ignition coils. Make all the connections clean and tight. This includes the harness connectors and the engine kill switch, both of which are exposed to the elements on vintage Hondas and which directly and dramatically affect coil voltage. If a later electronic ignition model watch for eventual pulser failure. Confirm a failing pulser by narrowing its air gap. Subsequent improved ignition performance spells the need for pulser replacement. The spark (transistor) boxes also eventually go. Test them by testing around them (pulsers and coils). Make your spark boxes last longer by avoiding starting attempts when the battery is low, which burns out the boxes. As for ignition coils, they actually fail the least often of the three main electronic ignition parts and are easily tested in place without needing tools, not even a meter. Make sure your plug wires are real wire and are tight at both ends, and have no unseen breaks inside the insulation. Change out the resistor caps when they exceed 5K ohms. If you have ignition wiring mods or repairs that include crimp connectors, humble yourself and make that stuff right. Change your plugs frequently.

Don't be a low-performance mechanic. That is, one trying to do so-called high-performance things that actually result in less than stock performance. Too many do this and don't realize it. Be a high-performance mechanic. Focus on intelligent, optimum stock performance that will result in high performance outcomes. Make sense?

Notes:

1 I hardly hear from anyone these days when ethanol doesn't come into the conversation, yet these same folks completely ignore cylinder compression, valve adjustment, and correct carburetor tuning.

2 There is also of course the supposed effect of different primary resistances on coil dwell saturation time and other esoteric ignition function considerations. But no one has proved this to be of any practical consequence. More a propeller-head's oscilloscope daydreams than anything, the much-debated primary resistance's effect on coil current eddies and such, thus engine performance, is not something that is noticed in actually riding the machine. No real-world difference.

3 I roll my eyes each time I see the phrase "Dyna coils" in a forum member's list of "modifications", or when a customer includes it in the same way in a conversation.