Is (extra) resistance futile?

[Ranburetta]

I have been using a Denso resistor type plug with recently fitted electronic ignition (a) because that is what is recommended by the manufacturer and (b) I have read that the CDI may be damaged if a non-resistor plug is used.

I don't have a SIP speedo or other similar component so that is not an issue.

I have recently changed the plug cap to one of the NGK red silicone type and I now see from the packet that it is a resistor type cap.

I understand that the resistance of both the plug and cap are 5 ohms, so plug + cap = 10 ohms?

My question is whether using a resistor plug and resistor cap together is likely to case a problem or should it be one or the other?

[Fast n Furious]

Normally "R type" Leads, Caps and Plugs have a series resistance of around 5Kohms each.
This resistive suppression only needs to be in one of these components. Any more will reduce the spark voltage. Some motors from the factory do have both resitive leads and plugs to get them through RFI approval but it's overkill.
There are some rare plugs designed for use with inductive ignitions that have 1Kohm resistors.
I recommend copper HT leads, a non resistive Cap (LZFH) and an R type plug for CDI.
Resistive leads do strange things under wet and damp conditions with bikes and scooters so it's best to ovoid their use.

[HxPaul]

I was under the impression that using a resistor type plug with a magneto ignition cut down its ability to make a spark at the plug,this seems to confirm it...http://www.brightsparkmagnetos.com/faqs ... gnetos.htm

[Fast n Furious]

I was under the impression that using a resistor type plug with a magneto ignition cut down its ability to make a spark at the plug,this seems to confirm it...http://www.brightsparkmagnetos.com/faqs ... gnetos.htm

Quite right. It will. If you introduce a resistance into an electrical circuit you will limit that circuits performance. In this case, reduce the spark potential. It doesn't matter what type of ignition system it is.
Suppression is a trade off, designed to suppress the Radio interference without too much compromise to the actual spark. A legal requirement for road vehicles.

[Ranburetta]

Thanks both, very helpful.