Intermittent running power

[blankmownot]

My 2009 ZT Bad Boy mower with 27HP Kohler engine has intermittent power. It will be running fine and suddenly will loss power and starts running rough , then it will suddenly be running fine with plenty of power. Just change air filter and spark plugs. Used it last week with no problems. Do you have any suggestions as to the problem???
Thanks

 

[BlazNT]

Ok lets start with water in gas. That is what it sounds like to me.