High (rear only) CHT / EGT Temp Conundrum

[Dbro172]

Not many hours but from day one my rear cylinder #3 and #4 seem to be running real lean. Aero Sport built Superior XP O-320 D1A. I started with no sealing and by now everything is sealed up real well and things have got a bit better. washer behind # 3 cylinder. I drilled the jet from #42 to #40 which lowered CHT's about 10 degrees and EGTs about 100 or more but my main concern is the big spread.

The more I back off the power the closer things come together. And if I open her up to WOT there is a noticeble drop in EGT's, but i cant run like that or the rear CHT's rise too much. On takeooff at full power i can easily get all four CHTs at 400 or more until i back off the throttle.

Started at full baffle deflectors on the front and cut back to nothing, which really helped front cylinders in the climb. no induction leaks

I wonder if the extra vacuum suction from the ASA oil seperator could be a contributing factor?? (btw - no coke at 6 hrs.). My manifold pressure at idle is 14-15.

here are some photos - obviously the mixture distribution at about 75% is all goofed up... how too fix? (remove three of the probes)

see:

75% power (EGTs before drilling jet were 1500 plus)


Brief WOT (EGTs come down)


65% power


50% power


50% just rich of peak



How much can temps be expected to come down as engine breaks-in further?

Oh yeah - it hasnt burned a drop of oil in the first 7 hours.