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TKART magazine How To | The DELLORTO VHSH 30 carburetor tuning manual
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14 May 2021
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Impeccable dynamics and engine at top efficiency: when you go on a track your objective is always the same, to force your kart to achieve the maximum to go as fast as possible. And if by modifying the set-up you can have a vehicle more suited to your driving style in your hands, the right carburetion of your fuel system plays a fundamental role in trying to make the most of the engine's potential. In fact, the carburettor has the following tasks:
1. check the power delivered by the engine by adjusting the intake air flow as required by the pilot via the accelerator pedal
2. dose the right amount of fuel based on the amount of air sucked in to maintain a correct air/fuel mixture ratio over the entire operating range
3. mix the air and fuel in the best possible way to ensure more efficient combustion inside the combustion chamber.
How important it is for a carburetor to be efficient and well-functioning as well as correctly set can be read about in the article "Expert advice - Used DELLORTO VHSH 30 carburettor: what to check before going (and while you are) on the track". Therefore, the importance of carburetion in the search for maximum performance and the good condition of your engine, one immediately wonders which are the components of the bowl/needle carburetor, in this case the DELLORTO VHSH 30, that affect carburation adjustment. Among these we find all the removable elements, that is, those that can be changed. Furthermore, carburetion is also conditioned by factors external to the carburetor which can be traced back to the type of engine/exhaust used, the environmental and track conditions, and the driving characteristics of the driver (driving with throttle or on/off).
The main factors affecting carburetion: removable elements, type of engine, environmental and track conditions and, finally, the driver's driving style.
Too lean carburetion can lead to engine seizure.
As we have detailed in the article published in the "Under Exam" section, the DELLORTO VHSH 30 is a bowl/needle carburetor that was created with the aim of ensuring excellent versatility of use, given the countless removable elements that can be interchanged to reach an optimal final carburetion. However, to better understand how these interact it is necessary to be clear on what, in general, the operation of a float/needle carburetor is, a subject already addressed in the article published in the "Tech Talk" section of TKART. In general it can be said that, thanks to the depression created by the air flow produced by the opening of the gas valve, activated directly by a wire connected to the accelerator pedal, and to the pulsations generated by the movement of the piston, a depression is created inside the diffuser which literally sucks the fuel into the same duct where the mixing takes place.
Going into more detail, however, a carburetor has several delivery systems, mainly 3:
1. the idle circuit
2. the progression circuit
3. the maximum circuit.
These different circuits of the carburetor come into play based on how much depression is generated inside the diffuser, a condition strictly linked to the opening of the gas valve. To simplify the discussion of the subject and understand how the individual components affect carburetion calibration, we just have to divide the latter into 5 phases that characterise all the possible operating conditions of a carburetor:
1. start-up
2. minimum
3. progression
4. stabilised
5. full throttle.
The various steps showing the operation of the idle circuit. The progression circuit is the same as that of the idle, only the outlet hole in the diffuser changes.
The different steps showing the operation of the maximum circuit.
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