Not sure which engines you have but I know on my 99 with the 800's when I have experienced water leaks from the exhaust the engines will not rev like they should. Check the welded bungs on the pipe there are several, they rot from the inside out, I have replaced all of them. I also recently blew the flange gasket and that exhibited the exact symptoms your describing. The tell tale sign is when you pop the drain, do you get a cup of water or is it gallons? I have worked very hard to only get a very small amount of water when I pop the cork. These things run like a mutt without proper water flow, so bad when I blew the gasket I couldn't even get the engine started, had to limp in on the starboard engine. use a mirror to see the ones on the underside of the head pipe.
