[TR] More on the yellow plugs

[Randall]

> So, cylinders 3 and 4 are rich at idle but lean when 
> cruising.  This doesn't make sense to me.

At least one possible explanation is that the jet and/or needle are worn.
The wear causes the idle mixture to go rich; then when you lean out the idle
mixture with the adjustment, it leaves the cruise (and power) mixture too
lean.  In effect, it alters the needle profile.

You might try swapping jets & needles front to back and see what effect it
has on the problem.

Another possibility is oil past the valve stems.  Tends to flow more in the
rear, because of the extra oil running back from the front.  Oil deposits
can also sometimes be funny colors (as can fuel).

Randall