You might have a fouled part in the carb. My 2 yr old 4 stroke Honda had some part destroyed by ethanol. The repair shop tried to clear the gunk or whatever blocked the passageway.... a very small diameter tube. They couldn't.
My engine would idle but I could not throttle up... it would sputter and stall. I replaced the carb and now it runs like a charm.
You should add a water fuel separator AFTER the bulb on the fuel line.
I was told to not store lots of fuel, use it and refill with fresh gas, and add fuel stabilzer. Apparently ethanol is wrecking lots of engines. I am not sure if it is worse for 4 strokes... but it hit me and I babied the motor.
I'd bet the carb fuel line is blocked.