lawn mower engines are the exact same as gocart engines, the only thing is that lawnmower engines are vertical not horizontal, if you are going to run a lawnmower engine on its side, it will not work, the oil will not flow right in the engine,
im no trying to be a fag by saying this, but if you dont know where the throttle adjustment is on the carb, maybe a little more research would be better before building one, because if you dont know this chances are there are more things you dont know..., just somethin to think about, but if you ever have any questions about gocarts let me know, my dad and i have built 10, 5 of which are racing and go 65mph (clocked with a radar gun)
as far as this carburetor goes, i need to know who makes the engine, should be briggs and stratton, robin, tecumseh or something like that, also, was it vertical? (meaning was it mounted in the lawnmower with the shaft pointing down, horizontal is when the shaft is horizontal) i need to know this so i can help you out