Sounds like one of your carburetor float needle sticking or a faulty fuel pump. I've had fuel pumps that when go bad, will not only pump fuel into the carburetors, but also pump fuel into the base. Take your plugs out and pull the engine over. If you have raw fuel spitting out of the plug holes... your base is probably full of fuel. You can ruin an engine in short order with fuel in the base. The raw fuel leaking from your exhaust manifold is likely fuel that is running into the engine (combustion chamber) through a faulty carburetor or pump. Also, pull your crankcase vacuum hose off the base and see if fuel is spitting out of the nipple when you pull the engine over.