I just went to winterize my boat (it is a centurion tournament boat with a 350 in it if that matters?)
I have done this for the past 2 years with no problem. I always like to crank it up to get all the anitfreeze everywhere while I pour it into the water pump.
I went to crank it in the garage today and it didn't want to start. Which is weird as it always starts with no problem. I gave it a bit of coaxing with the throttle and it went but then was really rough and black smoke out the exhaust. I have never seen this before? Smoked out my garage totally. Thought that I had started my truck in there and tromped it.
Pulled my water seperator and poured it into a container and the fluid looked to be 2/3 water and 1/3 fuel. Would this water and fuel mix cause all this smoke? I know that it will be rough but the smoke caused me some concern. I am going to drain the fuel tank but I am wondering now if I will need to take it right out to get it good and clean? Anyone else had this kind of problem at all? Any suggestions on what caused it or am I on the right track? Any ideas about fixing this problem? The only bad thing is now it is too late in the year to take her to the lake to run it and try to remedy the problem.
Any ideas/suggestions will be great.

The water probably coated the plugs so when they did eventually fire they had excess fuel in them Thus smoke. I wouldnt be overly concerned with it. Drain the tank and carb. It'll probably start right up in the spring with fresh gas. Don't worry over the smoke. I worked at a marina for years. Smoked the garage out a few times

x2 should be fine, gas engines take water pretty good.

if you have access to electric fuel pump jack up bow(trailer tongue) disconnect fuel hose to fuel filter, should get water first. oil companies put ethanol in gas after katrina(in iowa wholesaler/distributor each can put 9% in fuel without labeling) had lots of water in fuel afterwards, still do. treat gas with stabilizer all the time unless going to use it that week, Mercury buys gas for test cells and tests fuel and has told us lasts 2 weeks. make sure you fog topend good to keep problems from setting in.