Not that any of the other info is incorrect, but the first thing I'd do is go spend $2.50 for a new spark plug.
Just go to the dealer and get a regular factory replacement plug. Nothing fancy.. Talk nicely to them, and they might even give it to you..
I know it sounds silly, but plugs can and will go bad on 4 strokes.. My Honda Recon 4 wheeler was the same way.. Hard to start, backfired..
New spark plug and it starts instantly and runs perfectly..
It's cheap and somewhat simple. If that doesn't work, then start making changes..