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.
One man's junk is another man's treasure. I want to get a go kart now. The new ones are all stupid prices here, like $1000. I just want a plain old cart that takes mower tires. I want to have it for the winter so I can do burnouts and slides on the few snowy days a year in N. TX.