Seems the factory plug wires are just the length and size for most use.

 

Ever look at the spark plug wire length difference on a pre-coil over American V8. Some were 3 times longer than the others. Non issue I would imagine.

 

If you have the Delphi system ( ion sensing ), you will have to use HD stock sparkplugs, not the NGK's. I tried using NGK's on my 08 Softail with the Delphi system and it made the bike run leaner, hanging idle, better gas mileage etc. Lean wasn't good, so I went back to the stock plugs and the bike ran much better. Not sure if that's what you are running into or not. The difference in the spark plugs is what affects the ECM as it is expecting a certain reading, immediately after the plug fires. With the NGK plugs it doesn't get the reading it is program for, so it adjusts fuel/spark to compensate.

The HD's have a two post coil, so in affect each cylinder has its own coil, so the short lengths of the plug wires won't have any real affect. If the plug wires are 25 yrs old, it wouldn't hurt to replace them with new ones that work with electronic ignition.

At one time, before resistor plugs ( the R in the plug label ) the 5k resistor was in the plug wires, then they did away with that and instead built the 5 k resistance into the spark plugs. Even on the old bikes with the weaker coils going from 5 K to 10 K had no real noticeable difference as long as the wires and coils where in good condition. On the newer stuff with the hotter coils and better plug wires I can't see how a slight difference in plug wire length is going to affect anything.

 

If bike ran leaner and got better gas mileage with one manufacture plug over another. I would reset airflow in the ECU to match that plug. Sound more efficient. Hanging idle? Engine is able to rotate at a higher rpm with same amount of fuel and air. Sounds like a good thing to me.

 

Imho, there’s no need to use other than OEM plugs and wires.

 

Those years of bikes with the Delphi system didn't have an anti knock system as we now know it, so the system read the voltage just after the plug fired to adjust ignition/fuel to deal with what it thought was preignition. Those 96's were already running pretty lean from the factory and as to adjusting the ECU, I have no idea if that was even possible on those year bikes. I would think you'd have to disable the ion sensing system and then you'd be on your own as far as dealing with any preignition. Basically with the non stock factory HD plug it was throwing a code and the ECU was providing the wrong fuel mixture.

Much easier to just run it the way they built it. I just used it as a street bike, daily ride, long trip bike, so I needed it to be reliable and trouble free.

I just posted to this topic, to let folks know that even using a different spark plug can mess us the ECU's on these bikes.

 

So on an early EVO "86 sporty any wire will do?

 

And slso my late EVO '98 FLHRCI with MM injection, any good wire is fine?

 

For the evos, Harley recommends the regular carbon core wires.. No stainless steel nothing..

 

Without question trouble free operation with stock plugs and wires. No need to purposely add a variable (resistance) into the engine management system knowing the ECM has its own lookup table to determine combustion quality based partly on the plug and wire resistance.
Have found NGK 4179 to work ok and has a solid top like the stock plug so it can’t come loose and alter resistance readings.
Bob