It could be that you still have some moisture somewhere. Unless you bake the engine in the oven at 100 degrees for about an hour, it will take some time for all the water to evaporate out of it. Even if you use WD40 to displace the water. There are a lot of nooks and crannys that moisture can hide, including the carb.

I would remove the engine, take off the head and backplate and let it dry out for a couple days.

Another thing to consider is that when it flipped, you may have gotten a tear or pinhole in the fuel or pressure line(if using pressure). Also check the fuel line inside the tank for the same thing. Better yet, just replace it. Check the brass tubes for cracks also.

These may seem like simple things, but this turns out to be the problem for a not-so-right running engine, regardless if it was tossed in the drink.

I would check these things out before assuming you ruined the engine.