Jlg 450AJ with gasoline motor - will not run smoothly - could there be water in the gas?
Yes, but it could be a lot of other things too. You need to provide some more details on when it started running poorly, when it was last serviced, etc..
Engine not run for a while? Clogged jets, in addition to excess varnish build-up in carb.
Fred explains it well:
Very well could be fuel or an intake leak. How’s the spark plugs look? That can tell a lot.