An odd sequence of events occurred earlier today involving my 2gm20f that I hope one of the diesel gurus could clarify for me. I arrived at my boat today, a day following 2 days of strong north wind(25-40kts), to perform my ritual weekly crank of my trusty yanmar. I start the motor, let her warm up, engage the propeller in forward and bring her up to operating rpm while in the slip if I am not going to go sailing---it is far too cold for sailing this weekend. I have done this for the past 3 years that I have owned the boat. I follow all maintenance recommendations--usually doing things ahead of time. This motor has never, and I mean never, given me any trouble---it has rarely if ever not cranked on the first push of the starter button. Anyway, I arrived at the boat today, opened the thruhull, turned ignition on, and hit the starter button. Starter worked, but motor did not turn over after 1-2 seconds--odd for my motor. I went back downstairs and opened the engine compartment to "look at things". Everything seemed to be in order, there was no water in the engine room bilge. Racor had no water in it. So, I went back topside and tried to crank again. Motor tried to fireup after about 5 seconds of cranking but shook violently and then stopped. Went back downstairs and open engine compartment again and found an enormous amount of thick black smoke!! What!! After the proverbial smoke cleared(with help of an onboard fan) I also noted that now about 1/2 inch of water was present in the engine bilge. My first instinct was the mixer elbow, so I reached around to feel it. It was dry, however I did feel a bit of rust back there(I can't see back there in my boat). This was very alarming to me so I checked all hoses etc for leaking and found nothing--once again everything appeared to be in order. I went back topside and tried to crank again and after a bit of trying(1-2minutes intermittently) she reluctantly started---and ran well. No funny sounds, vibrations, smoke, water---like nothing at all had just happened??? I then ran her the normal 20 mins at 2500 in the slip without any hiccups, killed the motor, and restarted without any difficulty. Any ideas on what in the world all of this was? Do you think that maybe the strong north wind and waves somehow overfilled my exhaust?? But, my exhaust hose comes to the top of the lazarrette after exiting the muffler before exiting out the stern hole--a solid 3 feet. I would think that much rise would almost make it impossible to flood the muffler. However, the north wind does drive waves into my rear starboard quarter from across the turning basin in the marina. Any thoughts on this would be helpful as I certainly never want it to happen again. thank you very much, ken matejka