ran my boat today with 10/71s 12.8 at idle 11.7 mid range 12.5 wot lots of soot on the back of boat a little to rich ??

The only place it's rich is at idle. The idle could be leaned out into the upper 13's, but they typically wont have a very strong idle in gear unless they're as rich as you have it right now. 11.7 in the middle is good in my book, but the 12.5 is lean at WOT for a blower motor IMO. I shoot for 11.7 - 11.8 when solidly into the boost. A sooty transom usually indicates a nice safe tune-up on a blower motor. I always tell guys... it's easier to clean soot off the transom, than it is to scrape your pistons out of the headers.

i'm running 6 pounds of boost and you think 12.5 is a little to lean?

For a blower yes, at least in the drag racing world of tuning, I would think with the extended higher load even a little bit richer for a boat. I ran turbo and blower cars 11.6-11.8 and some thought I was running them too lean at that. But again I have no tuning experience on boats.

I do.

Like I said, I've always set up marine blower engines at 11.7 - 11.8 when into boost. Some guys like them richer than that...

Just got done freshening a pair of 675hp Keith Eickerts... 8-71's and EFI. They made 3.5 - 4 lbs. of boost and they were 11.4 - 11.5 anytime they were in the boost. I talked to KE himself at Lightning, and he said that's where they mapped them when he was doing them.

I run mine closer to 11.0 at the top end.

I would say; 11.8 is the max limit at WOT with 10 % ethanol. 12.8 at idle, is that in gear? Depending on drive prop dia. and pitch it seems like the engine would stall shifting into gear. What is your timing curve and type carb or carbs?

+1

Keep in mind a 02 sensor provides a "average" for the 4 cylinders on the bank its taking its readings off. On a carb'ed setup, certain cylinders may be leaner than others. So even though you maybe at 12.5 average, you may have a cylinder on that bank at 13 or higher. I think thats where the low 11 numbers really keep things safe. This way if your average is 11.2, that lean cylinder will still have enough fuel to stay cool.

was running 28 degrees total advance 36 pitch on the wheels still some tuning needed

aluminum heads? I would run a little more timing depending on the heads, 30 to 32 degrees.