Water in your vehicle's carburettor can cause serious problems. Water will prevent the fuel from properly combusting in the engine and can cause your vehicle to run badly or even not run at all, depending on how much water is present in the carburettor. There are several ways you can wind up with water in your carburettor; one of the most common is accidentally using watered-down fuel from a petrol station that has water in its fuel tanks. You can also get water in your carburettor by leaving your bonnet open in the rain or by driving though a flooded area. If your carburettor has water in it for too long, it will rust and you will have to replace it.
Rough Idling, Bogging and Surging
The carburettor's job is to create the ideal fuel mix for your motor and supply your vehicle with the proper amount of fuel. If the carburettor is supplying your vehicle with watered-down fuel, or just has small droplets of water mixed in occasionally, your vehicle will be getting a mixture that does not burn effectively in the motor. It will cause the motor run badly, bog down when accelerating or surge as the vehicle alternately receives good fuel and fuel with water mixed in.
The float in your carburettor may be damaged by water in the fuel. This tends to happen more frequently if you live in a cold climate and the water manages to freeze inside the carburettor and dents or damages the float. You must remove the carburettor from your vehicle to check the float, which controls how much fuel enters the carburettor and is used by the motor at one time. Check the float for damage if your vehicle seems to be getting too much fuel or too little.
Won't Start or Run
If there is a large amount of water in your carburettor your engine will not run at all. Engines require a combustible substance in order to start up and fire; since water is not combustible, too much of it will completely prevent the motor from operating. A large amount of water can enter the carburettor if the motor is accidentally submerged, which can happen if you drive through a severely flooded area, attempt to cross a creek offroad or get in too deep when you are launching a boat or canoe into the water. This can also happen if the vehicle's hood is up when it starts raining.
If your carburettor is rusting, you can bet it has been exposed to water at some point. Several pieces inside the carburettor can rust and cause different symptoms; check for rust if you are having any kind of carburettor problems.