Resistored Plugs and Caps

[bulldogbobby]

In the process of trying to figure out why my A4 isn't running better and not sure if this has been covered before but thought it might be of interest to others?

I 'upgraded' my standard NGK plugs for iridium ones (which are resistored) and replaced the caps with 'resistor - type' new ones. I've since been told that using resistor type plugs with resistor caps together will cause weak sparks and this is the reply I got back from NGK technical:-

Providing the ignition system is in good condition, having resisted plugs fitted along with resisted plug covers will actually give a stronger spark.

A visual check of spark outside of the cylinder is not a true indicator of the running conditions, mainly as voltage will rise only to the level that is required to generate the spark in the conditions surrounding the electrodes, i.e. outside the pressurised environment of the combustion chamber, the voltage rise requirement would be far less then when the plug is installed in the engine.

There should be no issue in running BR8EIX along with YB05F in your bike

At least I can rule that out now

[Hard Road]

if you earth a plug on the head on a 1200 bandit the spark looks week, but the engine runs perfect, you can't always rely on the spark you see.

[warren3200gt]

Resistored plugs and caps are fine in a modern ignition system.
In a ignition system that's designed and with components that are 50 odd years ago it's a totally different scenario.

The ONLY reason Kawasaki put a resistor in the ignition line was to suppress interference of analogue TV and radio signals. As the TV and radio waves are digital now there is now reason to use resistance at all.

You need to give your vintage ignition system every advantage you can. I know from experience that every vintage bike I've owned they ALL run sooooo much better and cleaner with non resistor plugs and caps.

With one resistor in the line they run OK, with two they misfire and have have lumpy idle and sooty plugs caused by a weak spark.

If you have a miss fire or lumpy idle try it with no resistance in line.

[bulldogbobby]

Resistored plugs and caps are fine in a modern ignition system.
In a ignition system that's designed and with components that are 50 odd years ago it's a totally different scenario.

The ONLY reason Kawasaki put a resistor in the ignition line was to suppress interference of analogue TV and radio signals. As the TV and radio waves are digital now there is now reason to use resistance at all.

You need to give your vintage ignition system every advantage you can. I know from experience that every vintage bike I've owned they ALL run sooooo much better and cleaner with non resistor plugs and caps.

With one resistor in the line they run OK, with two they misfire and have have lumpy idle and sooty plugs caused by a weak spark.

If you have a miss fire or lumpy idle try it with no resistance in line.

Brilliant - thanks mate

[warren3200gt]

Just found a simple diagram that shows the effect of resistance in the ignition system.
Volts are constant from the coil (because its unchanged).
Amps (current) are required to jump the spark plug gap.
Resistance (ohm) is the restriction of current flow not voltage flow.

So it's simple to see a higher ohm resistance in the ignition system will require a higher voltage from the coil to produce the same spark strength. Therefore, as the coil voltage output has not been changed, increasing the resistance in the ignition line means that it's harder for amps to flow creating a weaker spark.

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