"Reading" Spark Plugs
 

ok so i know that when i pull the plugs on a motor, white indicates lean, brownish is a clean burn, and black is rich...... my question with a rotary tho is will premixing cause the leading plugs to be black? i pulled mine today as i was going throught all the routine steps to get my FD back on the road for summer, and the leadings were both black, while the trailings were both PERFECT. is this normal?

fwiw i use amsoil premix, 1oz to every gallon of gas, not running an OMP. plugs are 9's all around, single turbo seeing low 11's afr @ WOT

why balck, why tan color *reasons*
 

yes, the physical properties of heat retention around the plugs dictates that what you have seen is correct and normal.

Reasons:
L plug hole (fully open hole to combustion chamber) is fully exposed to AFR mixture, it runs alot cooler than the trailing plug hole and generaly you need to run a hotter spark plug in the leading hole for this reason which alot of people dont comprehend.
T plug hole (small pilot hole to combustion chamber) will give you a nice indication of what is happening, even on a mates 600rwhp water inejected 13B street car runnng at 10.5:1 AFR with lots of wot running and not much idle you will see the colour pattern you described in your post. If you step down a few ranges in the leading plug it can then warm up the body enough to start to burn of the deposits on the plug body but it does not happen unless you get the heat range right.

In short nothing to worry about with the leading plugs looking blacker (no brownish indications), its just a function of the plug running alot colder rather than any fundamental problem with your tune up ;)

thanks for the good read :) answered my question and then some!