All the same symptoms. I replaced the plugs, filter and fuel with no luck. Then took the carb apart and cleaned it as well as I could, still no luck. Took it to a shop where the carb was torn down and heavy duty cleaning, it ran for the rest of the season, then in the spring the problem resurfaced. More trips to a shop and finally a new carb. It has been doing well since. There were two separate shops involved as the first one gave up. I was also in constant contact with the maintenance supervisor for Tohatsu USA. All along I have been using StaBil and fresh fuel about every month. The bottom line as best I understand it is Ethanol compounded by buying gas all over the place in small quantities. Of course when cruising you can't be choosey and what you get has been sitting in the hose between the nozzle and the pump where it can pick up crud from the real long hose.

Don't know if this helps, it is just one persons experience and the corn lobby wants to go E15.