Most go-karts use #35 or 420 chain size, while some dune buggies and ATVs use #428. Here's a great rule of thumb for determining go-kart chain. Even though some go-kart chains have the chain size indicated on the chain links, many others do not. If yours does not, then count the teeth on your kart's clutch sprocket.
If your kart has an 11 or 12 tooth clutch sprocket, it probably uses #35 chain
If your kart uses a 10 tooth clutch sprocket, it probably uses 420 chain