Spark plug cap... good vs bad ?

[hoogerbooger]

I have a cheap rubber non-suppressed spark plug cap like the picci attached, on my B40 star...running 6v and old style ignition.

a) is unsuppressed more important on 6V to minimise power loss/ maintain a good spark ?

b) would a different cap provide any real benefit ?

[JulianS]

That pattern is not very good quality in my opinion. Steel internals.

I think the NGK and black Champion (red Champion same shape is resistor type) unsuppressed are much better quality. Brass internals. The Champion one is waterproof.

Your bike would have been factory fitted with a suppressed cap.

[hoogerbooger]

Ok will get a better quality cap.

So does it really not matter whether I use suppressed or unsuppressed?
(In terms of  running/good spark.....as opposed to radio interference etc)

[JulianS]

I seriously doubt you would notice any difference.

Dont use a suppressor cap and a resistor plug at the same time though.

[chaz]

just as a reminder the NGK resistor plugs have a R in ie BR6ES , un surpressed would be B6ES

[Blackthou]

Very intersting. I didn't know there were such things as resistor plugs. What are the effects of having both in operation? How is any sort of resistor detrimental?

[Mike40M]

It all started when car radios became more frequent. RFI (Radio Frequency Interference) emanating from ignition systems, became a problem. Later when electronics became more common in vehicles, RFI problems got worse.
The solution was to put an resistor in series with the spark plug. Usually about 5000 Ohms. Three ways came into use. Resistor spark plug cables, where copper wire was replaced with graphite. Quite unreliable. Resistor spark plug caps. Last came resistor spark plugs. You shall not combine resistor spark plugs with resistor caps or resistor cables.
Different types of ignition systems should either have resistors or not. I've read that Magnetos don't work well with resistors. Coil and breaker systems can work with or without resistors. Different opinions on which is best. Some electronic ignition manufacturers say that they should be used.
I've read that NGK recently discontinued at least one type of nonresistor plugs common for classic motorcycles.

[AWJDThumper]

For classic bikes, non-resistor plugs and caps are best as they deliver the maximum spark energy - for these bikes, there is absolutely no need to worry about RFI provided you don't operate electronic devices as you ride along! 

[chaz]

dont forget, the resistors also stop interference on tv's , more of a problem than radios in cars. this was the problem back in the sixties watching tv, you could tell when bikes or cars without the resisitors went past

[JulianS]

Some spark plug photos, all used in light alloy A10 head.

On the left the conventional Champion N4C. Non resistor.

Top right Champion N4G, Gold Palladium type, non resistor, slightly finer electrode than N4C, the super plug of the 1970s and no longer made.

Middle right Denso IW22 iridium resistor type. Note very fine centre electrode.

Bottom right NGK BR7EIX iridium resistor type. Fine electrode, slighly thicker than the Denso IW22.

The A10 ran very clean (compred to either Champion) with the IW22 and non suppressed cap but they are quite expensive to buy and did not last very long, maybe did not like the magneto.

The A10 was not happy with the NGK.

[AWJDThumper]

dont forget, the resistors also stop interference on tv's , more of a problem than radios in cars. this was the problem back in the sixties watching tv, you could tell when bikes or cars without the resisitors went past

TV interference was a problem in years gone by but is no longer an issue with the switch from analogue to digital transmission. Also, from a mitigation point of view, there are so few classic bikes on the road that any interference caused would be fleeting and not worth worrying about.

[hoogerbooger]

As I have a near neighbour who is a radio enthusiast and has what looks like a NATO listening station towering over his house, plus a neighbour who has berated me about the loudness of the pattern exhaust( who by sod's law will probably turn out to be a CB radio buff)  I may play safe. (Will make up 2 leads one with suppression one without, to convince myself a suppressed cap will be fine)