Too rich or vapor lock?

I would guess that if you have been running excessively rich, the plugs would have been sooty.

You do not have a thermostat so the CHT is going to be cold.

I can only guess at the EGT but will mention that there is a large water jacket surrounding the exhaust ports of the head.

Cool Head, Cool Exhaust???

If you are right on the hairy edge of the mixture, moving the clip will either make it go away are make it terrible.

At least then you will know you are on the right track.

You have to do something to resolve the issue.

Make it leaner or richer, it will either Cure it or Kill it.  50/50 shot.

Have you tried isolating ignition systems one at a time?

The CHT and EGT temps seem low. I usually see 190 to 215 CHT and 1450 to 1520 EGT, OIL 215 to 225 , with coolant (thermobob) thermostat and mocal oil thermostat.  I am thinking you are rich , if it is a fuel issue. Me... 912 uls, KF 5/Outback, Airmaster prop.