21mm carburetor

21mm carburetor motorcycle moped scooter

Feature 21mm carburetor

21mm carburetor Works great for Puch, Motobecane, Sachs, Garelli, Peugot and more (JOG50 JOG90 BWS100 RG50 DIO50-90,for 50CC-100CC motor)

Details 21mm carburetor
Details 21mm carburetor

Material:Aluminum Alloy
We Have This Type Carburetor For PWK 21mm 24mm 26mm 28mm 30mm 32mm 34mm. Easy Install. You will get exactly as shown in the picture above


21mm carburetor Overview

The carburetor must be chosen according to the characteristics of your engine. If your priority is to increase the performance, the choice of the venturi diameter is fundamental because it affects the resistance that the aspiration system provides to the aspirate flow, in particular:

The larger the venturi diameter is and the lower the pressure drop will be than those with a lower venturi diameter and with equal characteristics with consequently power increase.
The smaller the diameter is, the more the flow speed will increase improving the power output.

The Polini CP carburetor has slightly different dimensions than the more common carburetors. At the time 21mm carburetor of purchase it is therefore necessary to consider what adjustments are necessary for a proper assembly. The most important adjustments are the flanges to fit the filter and the curves to connect the throttle cable and choke.

Filter 21mm carburetor
Filter 21mm carburetor

Once you have assembled the carburetor it must not hit or get in touch with other engine parts or bikes parts (except for the intake manifold or the filter to which must be connected). The Polini CP carburetor is sold with standard calibration that has been set-up during the tests on the most famous standard motorcycles and scooter or equipped with power unit but whose engines do not exceed 12.000 rpm.

For different settings see the proper section. If your engine exceeds 12.000 rpm and it is equipped with racing products we advise you to carefully read paragraph 11 “COMPETITION”.

Polini CP carburetor is of needle type.
The fuel arriving from the tank is held inside at a constant level thanks to the floating needle mechanism. The fuel level in the bowl that arrives to the jets during its working remains constant and therefore so it is the gap that the fuel must pass to get into the spray nozzle.

The fuel level in the bowl is therefore a calibration element of the carburetor, since when it changes consequently the signal on the carburetor intake nozzles changes and therefore affects the mixture ratio.

The adjustment of the level in the bowl depends on the float lever arm/needle and the weight of the float itself:

The floating needle lever arm is not adjustable in the POLINI CP carburetor. It is calibrated during its assembly and it can only be controlled. (See photos 1 to check the float measure). By installing a heavier float, the result will be a richer mixture; on the contrary, with a lighter float the carburetion will be poorer.

Information 21mm carburetor
Information 21mm carburetor

The floats are classified according to their weight and they should be placed inside the bowl according to precise provisions in order to achieve the best working. If you use special fuels make sure that the synthetic rubber at the ends of the needle is compatible with it. The diameter of the needle housing is another important element during the tests for the carburetor setting because it fixes the fuel quantity and its speed when entering in the tank, in particular:

• if the diameter is too small you risk to get a poor carburation because the bowl may empty very fast than the needle can make the fuel pass through, with the serious risk of damaging the engine.
• The diameter of the POLINI CP carburetor needle housing has been studied to avoid this problem as the hole diameter is oversized.


It is an adjusting element that determines the area actually available for the flow passage. It’s a cylindrical valve that slides across the venturi in an appropriate housing obtained in the carburetor. To eliminate the phenomena of wear or “sticking” of the throttle valve, the same and the elements that surround it are subjected to material hardening treatment.

The working principles of all the carburetors refers to the same physical principle. The principle is that the fuel responds to a vacuum signal generated by the induction action of the engine. When the gas valve is closed, or nearly so, the depression that insists on the main spray nozzle is not sufficient to draw fuel from the bowl. It is for this reason that the carburetor has a second supply circuit that operates with this kind of conditions (at IDLE) allowing the engine to operate normally that otherwise would stop running.

The idle circuit 21mm carburetor is equipped with a supply port placed immediately downstream of the throttle valve, at a point such that once the valve is closed, it experiences strong vacuum conditions and therefore is in the best condition to supply fuel from the bowl.

Size Information 21mm carburetor
Size Information 21mm carburetor

It is equipped with its own jet (idling) whose choice is very important not only to work in idle conditions but also to get the best engine response during the first opening of the throttle valve, which subsequently will characterize the next progression.

If the selected idle jet is too big, the engine may tend to stall and responds slowly to the throttle. If, on the contrary, the jet is too small, the engine responds better to the throttle but when the throttle is closed, the speed remains high for few seconds before settling down to idle.

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