The carburettor is one of the main parts of a vehicle. Its job is to regulate the speed of the engine. It does this by measuring the amount of air necessary for the speed at which you wish to travel: it pulls a small amount of air and fuel for low speeds, increasing that amount as you speed up. A flooding carburettor can lead to serious problems, but you can prevent the problem by learning about some of its potential causes.
Dirty Fuel System
Over time, the fuel system will clog due to debris that accumulate in the carburettor. When that happens, it's time to clean the carburettor. Turn the engine off before removing the air filter cover. Place a towel, or some other protective material, around it to ensure the carburettor cleaner you're about to use doesn't spread to other parts of the engine. Once you apply the cleaner, use a wire brush to clean the excess oil that has gummed around the carburettor.
Excessive Fuel Pressure
A normal fuel pressure is 2.95kg. per square inch. High fuel pressure--usually due to a fuel pump that's defective or worn--can cause carburettor flooding. Check the fuel pump, or if you lack the expertise to do it yourself, seek a professional opinion.
According to the pmocarb.com, the defective float problem develops when the tang (the metal adjustment on the float) is too long and catches on the webbing part that supports the stanchions on the float pin. To solve the problem, shorten the tang, then readjust the float drop.
You will occasionally need to replace the floats on the carburettor. After making such a replacement, compare the old floats to the new ones. Make sure that the pontoons--the parts of the float that actually float in the liquid--are in right relation to the hinges so as to reduce the level of friction with the float chambers.
If the engine is shut off and the fuel is dripping down the carburettor, it could be because the fuel line is too close to a radiator hose, an exhaust manifold or another source of heat. The heat causes the fuel--a liquid--to expand past the needle and the seat, which results in flooding. Have a professional investigate this problem.