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Reading the Plug

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WHen the outside of the plug is rich black and the inner core and tip is ashy white, what is the plug trying to tell me?

I am running a 2002 Honda CRF450 with the following:

FMF Factory 4 Exhaust

JD Needle Red (4th clip position)

42 Slow Jet

178 Main Jet

PowerNow Valve

Fuel Screw 7/8 turn out

KBB Valve Set and in spec.

TwinAir Carbon protected Filter lightly oiled

500' Above Sea Level, 90 degrees, humid, MX

Thanks,

Phil.

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additives in modern fuels give false plug colors.the plugs in my bikes always look "lean".

but they make max power on the dyno and the CO and A/F readings are perfect.

you will do nothing but chase your tail trying jet by plug color.

the only thing i look for on the plug any more is signs of detonation.

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You should be looking at the inner core, but as burned said, the reading is difficult to evaluate and be conclusive.

You can ride with different settings to get a "feel" for richer and leaner jetting or have a shop set the mixture with a CO meter. In general, the jetting you posted is close to what others use in your conditions (try a #175 MJ). The humidity and temp will favor leaner settings and a #40 pilot jet could be used to get the fuel screw closer to 1 1/2 turns out.

Thanks,

James

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