Carburettors are devices used in internal combustion engines to mix air and fuel in the correct proportions for combustion. The components, like the pilot jet, main jet, jet needle, and float chamber, play crucial roles in achieving the optimal air-fuel mixture.

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The pilot jet and main jet are responsible for controlling the flow of fuel into the carburettor’s mixing chamber. The size of these jets determines the amount of fuel delivered at low and high engine speeds, respectively. The jet needle, also known as the needle jet or metering rod, adjusts the fuel mixture based on the engine’s intake negative pressure and flow rate. It moves up and down within the main jet to regulate the fuel flow.


The float chamber is a reservoir within the carburettor that holds gasoline. It utilizes a float mechanism to maintain a consistent fuel level. The correct fuel level is essential for the precise functioning of the pilot and main jets, as well as the overall operation of the carburettor.



Keystar’s valve seat restoration kit is a product that offers a solution for replacing the valve seat in a carburettor. The valve seat is a critical component that helps create a seal between the valve and the cylinder head. Traditionally, valve seat replacement was considered difficult or unrepairable due to being press-fit. 

However, Keystar’s kit provides a means to replace the valve seat, allowing for previously challenging or impossible repairs. This innovation has gained attention and is regarded as a groundbreaking product.

Carburettors are devices used in internal combustion engines to mix air and fuel for combustion. This information explains the mechanism of how gasoline flows into the float chamber and how the float regulates the fuel level.

Oil Level

When the oil level in the float chamber rises too much, it can lead to overflow. Overflow can occur due to various reasons, such as foreign matter caught between the needle valve and the valve seat or wear on the mating surfaces of the valve components. 

If the carburettor has an overflow pipe, excess fuel will flow through the drain pipe at the bottom of the float chamber. However, some carburettors, like the Keihin CVK, do not have an overflow pipe. If the oil level rises excessively, gasoline can flow into the venturi and enter the engine or the air cleaner case.


It is essential to address overflow issues because if gasoline continues to overflow into the engine, it can dilute the engine oil, which can cause damage. Overflow prevention is also crucial from an environmental perspective to prevent gasoline from leaking into the atmosphere.

Replacing worn-out components, such as the needle valve and valve seat, can help stabilize the fuel level in the float chamber. Regarding carburettors with removable valve seats, Keystar’s fuel adjustment kit provides replacement needle valves, valve seats, and other necessary parts. However, it’s worth noting that the valve seat of the Keihin CVK carburettor is a press-fit type and may not be available as an individual part.

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In summary, carburettors are crucial in regulating the fuel-air mixture in internal combustion engines. Overflow can occur due to various factors, and addressing it is essential to prevent engine damage and ensure environmental safety.

Source: Young Machines

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