The left cylinder on my 2009 V7 runs roughly 75 F (24 C) hotter than the right.  Oddly, the left spark plug is dark, darker than a normal plug, showing that the hot cyl runs a little rich.  I've heard that running rich can cause overheating, but I've got no experience with that phenomena.  Any ideas?

The right side (cool side) plug is a normal tannish-brown color.

Here's what I've done:
Checked both sides for air leaks in the intake
Switched out the ECU
Sent out the injectors for flow testing and cleaning
Tried the Offset Cyl function on MyECU


I'm also getting temperature spikes.  At 3,900-4,300 rpm sometimes the temp on the hot cyl will shoot up to 400-550 F (205-290 C).  If I change the rpm to either lower or higher, the temp cools off.

Anyone had experience with this?

Bobd,
Spark plug thermocouples.  Not the most accurate devices, but after switching them around, switching the connectors, etc, I feel they are on point.  Also, pinging at 4k rpm, and extra bluing on the "hot" pipe, confirms the diagnosis of the hot cylinder.

I've adjusted the spark advance on two maps, and hope to take runs with them, when the rain stops.
Joe