Reading the Plug

[Gato_Volador]

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.

[yamaha259]

I would say lean, but ask around some more. A good brown colour is what you want.

[Wayward Son]

i tells you that reading spark plugs doesnt do any good with modern fuels.

[Silver Surfer]

this spark plug atlas has every state of plug... 😢http://www.dansmc.com/spark_plugs/spark_plugs_catalog.html

i tells you that reading spark plugs doesnt do any good with modern fuels.

burned, can you please elaborate on this???

[Wayward Son]

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.

[Wayward Son]

notice the info on that page is on a phamplet from 1977.

[Gato_Volador]

Forgot to mention I am using regular High Octane 92 pump gas.

Thanks for the responses

[James_Dean]

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