I/O cuts out when trying to kill it and water is suck up in the motor, had to take plugs out to get water out?

Question

I was told the problem is exhaust flapper letting water in. If that is it how can I check them to see if they need to be replaced?

Answer 1

That is one possible problem, but first what make and engine and boat are we talking about.  Just edit the question!  You can also have a timing problem, that causes a "kick back, and I've seen that cause the problem you discribe.  On some boats the installation of the engine is very close to the waterline, so it dosen't take much.  Merc, OMC and volvo all have some system to prevent this.  I've seen flapper valves melted off, so the running history of this motor might shead light on the problem.  Good luck!