When a carburetor causes an engine to flood during start up, the fuel level is too high, or a vacuum break is not working correctly. Too high a fuel level inside the carburetor will cause the engine to run rich all the time. This can be noticed by a decrease in fuel economy, and perhaps black smoke coming from the tail pipe all the time the vehicle is driven. If you want to understand how it works, just remove the cover from your toilet tank and flush several times as you watch the water enter the tank. Carburetors use the same type of system on a smaller scale.
Floats can soak up fuel over a long period of time and become too heavy.
When this happens, the fuel level goes too high. Many technicians automatically replace a float during a carburettor rebuild, but if you want to check it, they usually weigh between 7 and 9 grams for a single float system. This is approximately the weight of four dimes. A faulty carburetor vacuum break is often the cause of a flooding problem. The vacuum break is mounted on the outside of the carburetor and its purpose is to open the choke slightly when the engine is first started.