Winnipesaukee is right about the float value, I had that problem with our I/O and it got it running again, although if you had the carb rebuilt last year I wouldn't think it should be a problem this soon...but give it a shot.
The other thing it could be is the water separator needs to be changed out. When they become full of water or sludge the engine tends to bog down and die. Cleaning out a fuel tank is not an easy thing to do and you could have easily missed some sludge or water.
The other thing to do with ethanol in the fuel is to keep your tank full. If you run for a half hour or so you've probably burned several gallons of fuel and that will leave room for condensation to form. I have read it only takes a couple of weeks for the phase separation to begin and once that happens there is water/sludge in the tank again. (If you put it away last fall and it wasn't completely topped off then it attracted moisture over the winter)
I have never tried Seafoam, Startron got my engine at least running again and this year I am running StaBil formulated for ethanol on the recommendation of the marina. It claims to prevent corrosion of aluminum fuel tanks as well as everthing else ethanol related.
Replace the fuel filter as well.
As far as being able to run it in your yard okay that wouldn't be unusual since the fuel problem will show up when you try operate it under load. It uses more fuel then and sucks in the bad stuff in greater quantities.
If all you paid for the carb rebuild was $300 you got off cheap! I had to have the 4 carbs on my 115 Merc Outboard rebuilt and it was just under $740!
Good luck
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