I think they have a weaker spark, the resistor has something to do with
cutting down on radio interference, you always find new older sets of plugs
at autojumbles, quite cheap too,

Steve.

Don't know, I've never used them. That's why I asked.
I do know they're used to reduce radio interference.
Modern electronic ignition systems are supposed to put out more voltage so
should cope with the additional resistance. Don't know about the old systems
though.
I remember that we all used to throw away the old carbon string HT leads
because they had a high resistance. Replacing them with copper leads was
supposed to improve the performance. I did it just like everyone else but
never really compared the results properly.
Has anyone used resistor plugs with normal (old) Mini ignition?

John