POLINI carburetor kit with PHBL 24 mm and 3-hole rotary slide intake for Vespa PK XL
The rotary slide intake manifolds for the smallframe engines offer the possibility of using carburetors up to 24 mm. This means that quite powerful engines can be realized, which can easily reach the 120 km/h mark. In order to achieve the full performance potential of the engine, the engine housing should always be adapted to the cross-section of the carburetor (as far as this is possible).
Whether a larger carburetor and thus a larger intake manifold is necessary at all, however, depends on the displacement and the engine speed at which full power is to be delivered. A 133 cc cylinder (e.g. Polini) with a rated speed of 7000 rpm-1 is very well served with a carburetor cross-section of 24 mm. Using larger carburetor diameters on such an engine does not increase performance in any way and, in addition to the engine's economy, usually also impairs tunability.
Larger carburetors only make sense if the engine only delivers its full power at a higher speed (not to be confused with the maximum speed the engine can reach in third gear). One example of this is the 136 cc Malossi. This is already equipped with the direct intake kit with a cross-section of 25 mm. With a suitable exhaust and the rest of the engine design, this cylinder can also use carburetors up to 30 mm. We offer long intake manifolds from Zirri for such extreme tuning variants. With these intake manifolds, the carburetor is still in its original position.
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