3.5hp 4 stroke starts and idles, but no power

This is my first post. Sure hope you guys can help.
My 3.5hp 4 stroke has always run very well, with no problems whatsoever. I run it regularly, maintain it strictly in accordance with the owners manual, and have only used 93 octane gasoline with no ethanol. When finished, I always run the carb dry. One day it started on the first pull, and idled just fine, but when I began to open the throttle, it sputtered and died. I repeatedly started the motor, allowing it to warm up at idle, but could never get it to produce any power above idle.
The carburetor was removed and inspected, and found to be perfectly clean. Thoroughly cleaned it anyway. Reinstalled, but the problem remains. Starting to think it's not a carburetor, or even a fuel problem. What else could it be?

Most motors with your symptom have a fuel problem. That's a gravity feed fuel system, unless it's the newer model style that has a fuel pump. There's a possibility that the fuel filter is restricted. What method did you use to clean the carb? What does the plug look like?