I am running QFT M-800 dbl pumper carbs and they come with a 74 main jet in the primaries and an 84 in the secondary's. During the dyno session they were running lean in the 13s and 14's. They ran one wide band sensor on one bank. So, during the dyno I asked them if they would richen it up a little and so I now know that they increased the primary up to a 77 and the secondary to an 86. I am going to put the stock jets back in. Before my 02 sensors took a reversion bath, I was running real low 11's at idle and at mid and top end I really don't know because I couldn't read the gauge in the sun. I am assuming based on the plugs that were completely covered in soot, the 02 sensor the same and there is soot on the transom that it is in the low 11's or maybe lower at WOT. Is there a rule of thumb as to how much richer or leaner an engine will run when you go up or down a couple numbers in jet? Thanks for your help and comments.

Is it a safe bet you dynoed with long automotive headers and then put your marine exhaust on in the boat?
As for a rule of thumb for jet size vs A/F ratio not really. I'd suspect going back to your original jetting might be close though.

Jet size has absolutely nothing to do with idle afr

Yes but i think it was running very rich top to bottom. At actual idle it was in the 11's screws out about 1/2 a turn.

Yup. Long tube headers on the dyno. My builder said it would richen up with my wet exhaust. I got spooked looking at the numbers while on his dyno and asked to have it richened up. My mistake.

When I dyno a carbed engine with dyno headers with my huge semi mufflers in place, typically it still richens 3/4 of a point to 1 point in the boat with average entry level wet exhaust manifolds, IF your were in the 14s on dyno on top, that would put you in the 13s in boat which is usually too lean at wot. I would get your 02 sensors working before i made any drastic changes. As Griff mentioned, a rich idle has nothing to do with jetting. Buy yourself new 02 sensors, I doubt it was so rich it killed your sensors, water however will immediately kill sensors. Seeing your other post mentioning possible reversion, I would tell you to buy THESE: https://www.summitracing.com/parts/i...BoChHUQAvD_BwE
I have tested these on dyno and they do not affect 02 readings, they are directional so make sure there clocked correctly in your exhaust. They have allowed me to tune boats that killed o2 sensors that had some reversion, Smitty