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Hello all,
I would like some advice on changing my spark plugs. I have a Forty Eight 2014 with V&H 3inch slip ons, Arlen Ness Monstersucker. With all these modifications, which spark plugs will be the best?
I do not want to go for cheap, simply the best for my Sporty.
2008+ Buells and XR1200's came with the 10R12X, aka "SE Gold" plugs. They're colder than the stock 6R12's, and they also have a special insulator design that resists fouling. Part number 27794-08 at your dealer.
The company I used to be involved with sells a lot of big bore kits, I mean like a thousand a year, the majority of those for Sportsters. Detonation type failures are the bane of anyone in the engine kit business, believe me on that. When you sell that many engine kits, even a very small percentage of issues ends up being a huge headache. So they put a lot of effort into making the kits as robust as possible, and did other things like emphasizing proper tuning and carefully specifying how to tune it.
One of measures taken was testing a bunch of different spark plugs for their detonation resistance. The 10R12X plugs from HD won. So the company started specifying them for their big bore kits and including a pair in all big bore complete packages. They were (and are) not a suggestion, but instead a requirement.
Although they've been largely successful at driving detonation-related failures down into the noise, they still see the occasional detonation-related failure. But it's always the result of not following the tuning instructions. You can write instructions until you're blue in the face, but they mean nothing if they're not read and followed. Ironically, failing to tune per the instructions, and other failures to read the instructions like for example the head torque procedure, those mistakes are much more likely with shop installs. Do-it-yourselfers tend to not assume they know everything and therefore they read and follow the instructions. Shop techs, not so much. But I digress.
Anyway, just my .02, but the 10R12X plugs are an excellent choice for any motor with a bit of compression. And these late 1200's push the compression pretty hard, right off the showroom floor, between the 9.7:1 compression ratio and the really early 25 degree intake close timing of the stock "W" cams.
Last edited by aswracing; May 1, 2025 at 10:38 AM.
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Advice spark plugs Forty Eight 2014
