O-320 way rich after Major + 160HP conversion + Powerflow

The O-320 in our C-172 was professionally recently professionally overhauled
(at 2300 hours and 32 years). This included an STC to 160 HP, new
millennium cylinders, new crank (a story, there..), new cam, new carb, a
repitched prop, and a powerflow exhaust.

We're past break-in now, and the plane flies great, climbs awesome. The
recurring problem is that the carb is set way too rich. After a few visits
to the A&P (each time involving a lot of carb twiddling), it is getting
better each time. It is rich enough that I find that carb heat in the
pattern induced pretty good roughness and often backfiring. In fact, I find
that I need to keep it leaned even on the ground or in the pattern (our
field is only 200' elevation). On the ground, the idle is at 650 with the
mixture in, put pull it out about an inch or 2 and it gets a lot smoother
and a little bit faster.

The mechanic feels that it will take us a few iterations to get it set up
right, since there is so much new stuff here. He feels that the exhaust may
be a big part of this.

One other clue, the EGT now reads a lot lower than it used too. They are
apparently going to re-calibrate the thermocouple so it will at least
register on the gage.

Anyone have any experience like this?

Thanks,

dave