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Spark plugs


Well Known and Active Website User
VOC Member
I'm sure there must be a thread on this subject, but I couldn't find it, and I'm sure I'll probably get lots of different opinions, but what is the best plug for a mildly tuned twin, (8.5:1, 32 mm Mk1 concentrics, Mk3 cams, points coil ignition) for general social and touringish use?

I seem to be in a time warp, my Egli engine is more or less as it was in the 80s the current plugs are low mileage Champion N9Y, I seem to remeber using N5 and even N3 before settling on them, and I'm fairly sure they were used for everything from camping trips to Spain to High Speed Trials at Cadwell. The engine starts easily and runs well, but if there's a modern plug out there that will give me another 10 bhp or 10 mpg I might change.



Well Known and Active Website User
VOC Member
Here's two that I have been thrilled with...

Afternoon all,

It may come up by you searching carb problems, but longer time readers of the Forum will know I had terrible troubles with things on the "make it bang" side and eventually got some specialist help on spark plugs as part of the solution. I recall that that thread will even have the details of my web based spark plug specialists and supplier - they are thoroughly recommended.

I have ridden 2000 miles on Denso W20EP-ZU - they are no longer available but Denso may be able to sell you something to replace them, however they can come up at autojumbles etc from old stock if you look, non-resistor too. They are platinum electrode and I can't fault them. I have Pazon ignition and gap them at 28 thou.

I've also had good results with Denso Iridium plugs, bit more expensive and I use the IW20.

I tried Champion, tried NGK, tried projecting and protected electrode and settled on these Denso plugs. Until the IoM Manx GP when I got water in both floatbowls I had not lifted the plugs in 2000 miles and they looked perfect.



Sorry, the last part was a bit flippant, I'd seriously like to know if there's a more suitable modern plug. I notice they seem to be using various fancy metals for the electrodes now - I bet depleted Uranium would give a nice spark.


Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Iridium & other unobtanium pluge were developed mainly for long service intervals on modern vehicles. I've never tried a wonder plug that makes any improvement over a good quality standard type in normal applications. The only application that automatically NEEDS a fine wire Iridium plug in my experience are highly boosted turbo engines , but we're talking 400 BHP and above from 2 Ltrs !!

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