There is a machined fitting that Howell sells that will allow you to put in an O2 sensor on a boat. That is what I have. I put my water cooled manifold in a bridgeport, milled through the water jacket and right into the exhaust. I have a functioning O2 Sensor on the boat.

http://howellefi.com/adaptor-o2-sens...arine-use.html

I also remember that the other valve cover is connected to the air cleaner. My mistake.

Will the data inform me for sure that there is a vacuum leak? When it is first running, it idles down and the IAC count keeps fluctuating from 65 down to 35 or so as the motor comes close to stalling then corrects itself.

I will get to the bottom of this, as the boat should be running better than it is.

Thanks