Assuming that the float height setting is correct, the normal cause of flooding is a small amount of dirt (i.e. rust) lodging in the float needle valve, preventing it from closing. Fuel continues to fill the float chamber, eventually overflowing or ‘flooding’. The cure is to remove the float lid and clean out any dirt from the fuel line/needle valve and reassemble. The main cause of dirt in the fuel is from residue or rust in the fuel tank. A temporary fix would be to fit an inline filter but a clean tank is the only real solution.
Another cause of flooding, often mistaken for an over high fuel pump pressure, is caused by air trapped in the float chamber. When fuel is fed into the float chamber it rises and the float shuts off the needle valve. If, however, the chamber air vent is blocked, the fuel rising compresses the air in the chamber and fuel is forced out of the jet at pump pressure.
There are several different methods of venting the float chamber, from a simple hole in the lid to overflow pipes, all of which can be blocked in various ways. If in doubt, loosen the fixing of the float lid just enough to allow air to escape and see if this cures the problem. If it does, then hunt down the blockage and remove.
