[TR] More on the yellow plugs

[Adrian Jones]

The plot thickens.
Plugs 1 and 2 are OK.  They have brown deposit after a run or after idling.  Colourtune shows a blue flame
at idle.
Plugs 3 and 4 have yellow deposit (not tan) after a run.  Colourtune tune shows yellow flame at idle and plugs become sooty.
So, cylinders 3 and 4 are rich at idle but lean when cruising.  This doesn't make sense to me.
I checked for air leaks at carb/manifold and manifold/block but everything is fine.  Also, no cracks in manifold.
I can't see how the ignition could cause this.  Re-checked valve clearances and everything OK.  Disassembled carbs - everything appears OK.  All I can think of is maybe the water ways are blocked around 3 and 4, causing localised overheating, or is that too stupid.

Adrian, driving a Toyota in sunny NC