Dave what is C advance? Are you talking about timing? If thats the case then no I did not change anything with ignition. I went to the boat today and tried the test that Neil has suggested. I had a helper holding a thumb to close hose that we have disconnected from the PCV valve. Still had the same issue. PCV valve rattles, so I don't think its stuck. As far as the carburetor is concerned I was looking for a vacuum leak, which is why I changed the gasket between halves. Old one did look somewhat warped. Dave, what did you mean when you said that:
"the throttle linkage holding the carb off of the idle stop"
How do I check for that? I looked at MM manual and only suggestions I am seeing are basically to clean up carburetor. Given my water intrusion earlier dirt in the carburetor is possible, but I've cleaned it after twice (one full and one partial). I wonder if anything else could be at play here. I really liked the possibility that it was caused by PCV, but I think my test ruled it out, right? That would have been a really easy fix