Quote:
Originally Posted by
WeaveMcQuilt
I tried an Iridium plug which was specified by my dealer as being the NGK CR7EIX.
I found it to be sluggish and choppy, and if it wasn't a single cylinder, I'd have said that one of my cylinders wasn't firing correctly... It felt like that.
I saw someone mention the same problem and he swapped it for the next plug in series, the CR8EIX which I did and it's a perfect plug for my bike.
Maybe because the engine burns hotter with the mods I've done, I'm not really sure but this did make a noticeable difference to performance.
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Interesting one that. I did read the same OP regarding CR7/CR8 debate (
http://www.xt660.com/showthread.php?t=21527 ) and did go away and give it a bit of thought.
The 8 is a cooler plug, which isn�t quite what you�d expect to need when you�re moving from the leaner A/F ratios in the 14s:1 of a stock bike to ratios in the 13s:1 on a bike with modified (richer) fuelling. Sluggishness, choppiness and misfiring are usually attributed to a plug of too cold a heat range resulting in fouling. Generally speaking, richer mixtures will result in lower cylinder head temperatures, so you�d expect to change (if you needed to) the heat range of the plug in the hotter direction to prevent fouling and maintain the correct firing tip temperature.
What I did find out is that the 686cc Raptor�s stock plug recommendation is a CR8 (with a 0.6mm gap rather than the XTs 0.8mm gap as recommended by NGK). Quads are of course not subject to the same emissions regulations as on-road motorcycles, and probably don�t run as lean or need to be as clean, so maybe there is some logic in using a CR8 on a modified XT? Conceivably the CR7 may only be recommended for emissions reasons, to suit the stock lean burning catalyst equipped motor?
Not tried an 8 myself, never had cause to, but perhaps in the interests of science and experimentation, I ought to give one a go�