So, to summarise (summarize):
5k resistance is good for supressing interference but you shouldn't use resistive plugs, caps and wires at the same time (?)
That's a good summary, I think. And, I might add that that is exactly what Honda delivered in stock form. I haven't found many extraneous, non-useful, parts on these bikes.
I spent many years working for Xerox and 3Com Corp., working on Ethernet, baseband, and broadband transmission systems. In later years, I found the knowledge gained working there, useful for eliminating both EMI interference and suseptability in PCB design and product packaging. As chip devices installed on PC Boards got faster and faster, so too did the rise times associated with these devices. Board traces had to be thought of as transmission lines or the rise time spike generated would radiate to other traces acting as receiving antennas. Or, into free air where the FCC, CSA, VDE an other countries regulatory organizations around the world objected to energy broadcast into their controlled space.
There are many techniques that can be applied to quiet PC boards besides physical barriers, which usually have an impact on packaging. One technique to quiet signal traces is wave shapping. Termination resistors do just that but reducing the spike or overshoot at the leading edge of the transmitted signal, thereby limiting the energy radiated outside the transmission line. The leading edge slope changes, and the energy spike lessens and broadens in duration. These effects can be seen with an oscilloscope. And, the shapes are the same regardless of the voltage levels employed by the linked devices. It is based on these lessons and experience that I confidently state that while the absolute initial peak of the spark impulse may be reduced somewhat, the duration of the spark pulse is broadened, when a series termination resistor is employed. And, while I haven't done the calculations to determine just how well matched the 5K specified resistor employed by Honda is to the impedance characteristics of the SOHC4 ignition system, I'm comfortable trusting them to that choice. Further, 10K ohm series resistance will make the waveform rise time slower, as well as excessively reduce the voltage passed to the plug gap. This can tolerated while the plugs are new. But, to maintain proper sparking, the plug will have to be serviced/replaced more frequently as their voltage needs will increase over time.
The zero ohm case will indeed allow higher peak intantaneous voltage at the spark electrodes. One drawback of this is that spark errosion of the electrodes increases. This will shorten the life of the plugs as the electrodes physically deteriorate more rapidly. The gap will increase over time, and approach ever closer to the maximum limit capabiliity of the coil. This peak will be of a narrow duration. I note that popular MSD ignition systems provide multiple spark pulses of increased event duration to fully involve the chambered mixture and help achieve complete combustion. I believe stretching the duration of the spark, rather than the peak of the spark to be a good thing.
You can actually put a lit match out by throwing it into a full bucket of gasoline. But, hold a match over it and whoosh. The difference here is the time it takes to ignite the vapors coming off the surface of the fluid.
The spark at the gap must hold the compressed fuel air mixture at ignition temperture long enough for the reaction to become self sustaining, whereupon it generates its own heat. What is better served for that purpose? A very short duration high peak event? Or, a slightly longer event sufficient to confidently instigate the combustion process?
Lastly there is the side benefit of the resitors reducing radiated emissions that can effect nearby radio and TV reception. Here, I expect those that like loud, noisy, pipes to be gleefull when they drive through traffic and neighborhoods, where people can not only be assulted by the invasive exhaust note, but clicks and pops on the their radios and interference lines in the their TVs, too. Such people will not want resistors in their ignition systems, as they enjoy the animosity and attention they receive in the process.
Frankly, I get enough of that without additional provocation.
Cheers,
