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1 July 2025 (updated) Car carburettor: functions, fault symptoms, and problems
A carburettor is a device with which a fuel-air mixture can be produced for a petrol engine. In the past, practically every petrol engine had a carburettor, whereas today at least larger engines (e.g. for cars) generally work with fuel injection. Engines with carburettors are referred to as carburettor engines (in distinction to injection engines) for clarification purposes.
How does the carburettor work?
The carburettor such as a Pierburg carburettor receives air through the means of a hose, which is previously filtered by an air filter to take out all of the grime. At the same time, a spout brings fuel into the carburettor. The air-fuel mixture is then fed via a valve into the combustion chamber. You may have to clean your car's carburettor if a lot of grime has collected in the pipe. If you don’t do this, the spout will clog up and keep the fuel from getting into the chamber. This impedes the combustion process, causing the engine to stop running as it should.
Carburettor problems
There are several problem cases that indicate that you need to adjust the carburettor. A carburettor may be dirty, causing blockages in the main jet. This results in the gas not being accepted properly. Leaks or a hanging slide are other causes of carburettor malfunction. Other typical problems are water in the fuel, corrosion and deposits in the carburettor engine. An incorrect mixture also impairs the function. Only if the idle speed is correct, the engine load is reduced and the throttle is accepted correctly. Fine adjustment via the mixture screw allows you to regulate the revs without the need for special tools. The throttle valve or slide valve are very important for proper functionality. The nozzle for the air supply must not be clogged. As part of maintenance, it may be necessary to occasionally clean the main jet, idle jet, and other components in the carburettor.
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Can a wrong mixture be recognised by the exhaust?
If white to light grey smoke comes out of the exhaust, the engine is overheated and the fuel mixture is too lean. On the other hand, if there is black, sooty smoke, the mixture is too rich. If the exhaust is brown to dark grey, this indicates that the carburettor is properly adjusted. The operating noises from the engine also help to identify the wrong setting.
Adjusting the carburettor
If you want to adjust the carburettor with a carburettor repair kit, it makes sense to first look at the individual car carburetor parts of this system. The fuel enters the float chamber, and the liquid lifts the float. This float presses against the float needle valve, which closes at a certain level. Now the maximum filling level has been reached. If the valve does not close reliably, there is a risk of the carburettor overflowing.
Basically, the carburettor engines of the various vehicles and devices are constructed similarly. You will find all the information about the engine in the operating instructions. Therefore it will be easier for you to interpret the symptoms. If you want to adjust the carburettor on the engine yourself, you only need standard tools. Therefore remove the car air filter, which is located in front of the carburettor on many vehicles. Use a flat-head screwdriver to adjust the mixture screw until the carburettor engine runs smoothly. This is the main work that requires a lot of attention and sensitivity but is relatively uncomplicated to carry out. In connection with the fine adjustment, synchronisation can be useful.
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