Now if I read things right one says run 10kΩwith 5kcaps and 5k plugs. Then one says 5k only. PLEASE I am not trying to start any trouble. I just do not understand What the will happen or show up as something wrong with it one way or the other.
There are a lot of configurations that will "work" for some value of work. The difference is optimization.
The "dual output coils" we use is technically a misnomer, as the "output" terminals are each connected to opposite ends of the same secondary coil of wire. When current flows through the coil, it flows in a loop, out one lead and back to the other, with the path being:
spark lead-
spark plug-
cylinder head-
spark plug-
spark lead. Once the spark gaps establish an arc, the only thing limiting the current in the entire loop is the resistance present in that loop circuit. Adding resistance will reduce the current in the circuit.
Why do we want this? There are several reasons.
One, is that it shapes the pulse waveform initial peak from a sharp spike into a softer rise. The energy is not lost. It is only delayed, stretching the duration of the entire spark event, allow the arc to be present at the plug tips for a longer duration, which allows more involvement of the volatiles being ignited.
Two, the coil itself has resistance. Passing current through a resistance generates heat. More current, yields more heat generation. Electrical insulation materials can become damaged with heat and the exposure time of the heat matters. In short, if it runs at a higher temperature, its useful life is impaired. Nearly all electrical components have a derating assessment associated with a rise in operational heat. This factor is included when calculating the MTTF (mean time to failure).
Three, the temperature of the electrodes has an effect on electrode material loss when the spark occurs. Each time the arc at the spark plug tips occurs, some metal is lost in the path of electron flow. The negative spark gap electrode is where the material is lost. If you have examined old spark plugs and compared them with new, you have observed the rounding off of any sharp edges, and possibly even noticed that the spark gap was eroded larger than when first installed. (I'm not talking about iridium type but the ordinary steel electrodes of our most-used NGK spark plugs.) The point of the spark is to generate heat above that which is present at the time of the arc. This is where the heat range of the spark plug comes in. A D7 is a hotter heat range than a D8, meaning the D7 wicks away heat from the electrodes slower, and allows them to run at a higher temperature. Reducing the spark current allows the hotter plug electrode the spark erode slower.
The 550 uses a D7 heat range plug, and I assert that is why the 550 bikes originally had 10K plug caps instead of 5K that the 750 and 400 used with its recommended D8 heat range spark plug. ( I believe you can find individual delivery variances, due to various reasons unrelated to technical idealism.)
In summary, it is the total loop resistance that determines spark current. It doesn't matter how many resistors are in the circuit as long as their individual values sum to the design goal. Four 5KΩ resistors in series results in the same circuit behavior as two 10KΩ resistors.
If you use two 5KΩ plug caps with D7 spark plugs, you can expect them to wear out more rapidly than if you use 5KΩ plug caps with DR7 spark plugs.
If you use D8 spark plugs, then 5KΩ plug caps would operate as intend for the expected maintenance cycle/duration.
As for using D8 heat range spark plugs in the 550, I say don't, purely because of the very poor cold/warm up operation. But, if you like to run the bike stationary while it warms up, they are "tolerable". But, If I were planning on a flat out run through hot desert county
THEN D8 would be a better choice.
