850M is about 2788 ft, if my math is any good...
With 27% ethanol and a 600 DP
Ima thinking, your jets are too big and
UNLESS you have eliminated the PowerValve, the split is too small.
I think those carbs new, are jetted closer to 66 front, and maybe 72 out back. I'm kindof guessing here; Your altitude adjustment is about Minus 1.5 sizes , and your ethanol adjustment for 27%, might be about Plus 1.5 sizes; so the OOTB jets should have been pretty close for a 318. So yeah, at #69 your plugs should be reading rich.
This goes along with your engine behavior between cold and normal. A cold engine needs to be richer than a warm one. So fatjets will help the cold running, but hinder the warm running.
(For comparison; I run 70/72s in the front of my 367 with a 10.5PV, at 930 ft with 10% ethanol.)
However; running rich should actually make the chambers run cooler. And that will make it burn slower. So not all that fuel is not gonna finish burning in the chambers, and so it will have to finish in the exhaust system, and come out the tailpipes very hot. And your meager 10* Idle-Timing is only gonna make it worse.
Again, However; you didn't give us any clues about your 318 build, nor the combo or gearing etc, so 10* on a stocker might be just fine.
If you have solid lifters for instance, your power-loss during the temperature swing, could be as simple as a too-tight lash setting.
I think if it was mine,assuming a lo-compression engine, and about a 2200 stall; I'd start the tune at 66/74 and plug in a 10.5 PV. Then increase the Idle-Timing to 14*, and limit the Power-Timing to 34@~3400. I would modify the Vcan to ~16* and bring it in ASAP. If solid lifters, I would reset to .018 int/.023 ex. Then see how it likes it. You may have to idle it up a lil to prevent a tip-in hesitation. I would block the secondaries closed and put a few hours on it until you get the beast base-lined.
IMO
there is nothing intrinsically wrong with 27% ethanol. If I could get it around here, I would retune my combo in a heartbeat to run it.
