What makes you think it is rich in the air?

I have seen people have multiple dead sticks swear they were tuned perfectly and 1/8 to 1/4 turn richer problem solved. Not saying that is your problem, but, anyone who tries to run rich so it sounds like a four cycle condition is asking for trouble. Guess what, you found it.

What are your needle settings?

Have any of those 11 experts tried tuning it from scratch.

I would get the best tuner to set it to what he thinks perfect is and try flying it that way.

IMHO a couple of cents worth.