Intake Leak

 The EGT was rising when I reduced power from 23" down to 16" when approaching an airfield.  It would go from about 1370 with a full rich mixture all the way up to 1550.  Pretty startling when I noticed it.  Enrichening the idle mixture mitigated the issue but it still rose to about 1420.  No idle cut off lean rise in rpm on the ground either.

Did a careful inspection and noticed that the intake coupler for cylinder number 4 was almost all the way off the intake manifold.  Almost an inch of tube was showing next to the crank case.  

Removed and installed a new coupler.  Cleaned and painted the intake riser tube.  Cleaned off the intake manifold face.  It was a few hours of work.

Now, without adjusting the idle speed, it idles at 520 rpm instead of 650.  Just a few more adjustments to do and I think it is all tidied up.