I bet it would work for a 3hp too. Just take the stock carb off and look to see what size hole it has, and how long it goes at that diameter. I have more details if you want. The bicycle cable-to carb makes throttle control easy to do!
I'll find an old go-kart eventually. I've got no cash for it now anyway. I like to collect stuff though. I almost had a go kart with a 3 speed tractor rear end, that would take vertical shaft engines, but I had to move before I could get it together.