i run cam 2 have 74mm high comp piston web cam, e-series system [pro-meg],400ex carb with 350x air boot. i have a 155 main jet runs ok it could run a little better. my plug after going through a 5 gears and checking the plug it was a dark tanish not ,more on the dark side.
should it be ash white ? and i have a lot of back fire at high rpms.

 

The general rule of thumb is: Tan is running good, Black is running rich, White is running lean. You usually want it tan.

~Team440ex

 

I agree. for normal riding a light tan/coffee color is perfect

 

most plugs i have seen are white and silver with little gold ngk letters

 

I lot of back fires at high rpm means your still lean or rich on the main jet though...usually a bit lean if it runs ok but hesitates slightly
rich if it feels like it is losing power.

warm up the bike
change the plug, and quickly (not letting it idle for amore than a few seconds) get it up to WOT and hold it there for 15-20 seconds in top gear(if you have the space) then, shut it down by pulling in the clutch and hitting the kill switch at the same time while holding it WOT.
coast it to a stop and pull the plug out and check the color

 

Does the rule apply to unleaded gas? I heard unleaded gas won't give you a proper plug read.

 

yes the rule applys to unleaded fuels

leaded or unleaded it makes no difference. you get the color from the heat of the combustion.

 

hmm sounds interesting this will be something I do when i get my machine running again I think it is running a little lean I get some hesitation in first sometimes!

 

I had the same question as wanabe, but now I have another. If the plug is closer to either white or black, which is better? I was always told that running a little rich is ok, but running lean is not ok.

 

I know this is basic stuff, but NGK s site had some pretty detailed info for diagnosing your plug color. You guys have probably all seen this before, but I found it helpful when learning to read my plug and trying to figure out what to do about it.

NGK spark plugs