90cc Chinese Quad Carburetor
In the bowl of the carb there is a hinged float. Where the float hinges there is a needle valve. When the fuel level drops in the bowl, the float drops. This in turn brings the needle down such that fuel flows into the bowl until the float is raised and the needle closes again. Sometimes these needles dont close all the way - either not adjusted correctly, get trash in the way, or just get stuck. The float can get stuck down such the the needle doesnt close too.
I got my daughter a sunl 70 from raceway. After I changed the oil. I lifted the frontend up all the way to tighten the drain plug. When I sat it down it began leaking through the overflow hose as you describe. (It was stuck open). I simply lifted the front of the four wheeler off off the ground and dropped it several times. It quit leaking because the float became freed.
Hope this helps,