POLINI SI24/24E – Production-Spec 24-mm SI Carburetor for Vespa PX200
Version with separate lubrication – solid stock-based design, but without internal flow optimization
The POLINI SI24/24E is a classic 24-mm SI carburetor for Vespa large-frame engines with separate lubrication. Polini sources the carburetor from Spaco/Dell'Orto; technically, it is a stock-style version without any additional internal machining of the fuel or air passages.
This makes the carburetor an excellent replacement for a worn-out or damaged stock SI24/24E and a solid starting point for classic PX200 setups.
However, it’s important to understand the distinction: The POLINI SI24/24E is not comparable to a BGM PRO SI24 or SI26 Faster Flow, which we extensively modify in-house. With the BGM PRO Faster Flow, the areas relevant to fuel delivery are specifically modified to ensure a higher fuel flow rate in performance-tuned engines. The POLINI carburetor, on the other hand, essentially adheres to the stock SI design.
SI24/24E
Ø24 mm
Separate lubrication
Spaco / Dell'Orto base
PX200
Stock jet settings are usually too lean for tuning
The POLINI SI24/24E at a Glance
Ø24 mm: classic SI24/24E size for Vespa 200 Large Frame
With separate lubrication: for engines with a stock oil pump
Spaco/Dell'Orto base: stock-style carburetor without additional Polini flow modifications
Fuel delivery close to stock: a solid foundation for stock and mildly tuned engines
Factory-set with PX200 10 PS base jet settings: HD 116, BE4, and HLKD 190
Re-tune for tuning: the stock combination is too lean for many tuned engines
Proven tuning base: HLKD 160 and BE3; select the main jet that matches the specific engine
Stock-like SI—not an internally optimized “Faster Flow” carburetor
Externally, various SI24 and SI26 carburetors look very similar. However, what matters is what happens inside.
The POLINI SI24/24E is a stock-like Spaco/Dell’Orto carburetor. Polini does not modify the internal fuel and air passages in the same way as a carburetor specifically designed for high-performance engines.
This is not a disadvantage for a stock-spec engine. However, with more aggressive tuning, the fuel delivery of the classic SI design can become a limiting factor.
POLINI SI24/24E vs. BGM PRO Faster Flow
| Feature | POLINI SI24/24E | BGM PRO Faster Flow |
|---|
| Base Body | Spaco/Dell'Orto SI | SI carburetor as a base |
| Internal Machining | Close to stock, no additional Polini flow modifications | Specifically modified in-house for higher fuel flow |
| Primary Application | Stock to mild tuning | Performance-oriented SI engines with increased fuel consumption |
| Tuning | PX200 base jet setting close to stock | To be adjusted to the specific engine setup |
Factory-set with German PX200 10 PS basic jet setting
The carburetor is supplied with a basic jet setting very close to the stock configuration:
Main jet: 116
Mixing tube: BE4
Main air correction jet: 190
Secondary jet: 50
This combination comes from the stock-like setup of the German PX200 with 10 PS. It works exactly as intended in that stock configuration.
However, this jet setup should not simply be carried over to a 200-cm³ engine with increased power. In particular, the combination of the HLKD 190 and BE4 mixing tube is generally far too lean for standard tuning.
Why the HLKD 190 and BE4 Are Problematic for Tuning
The main jet system of an SI carburetor consists of more than just the main jet. The main air correction jet, the mixing tube, and the main jet work together to determine the fuel delivery across the relevant load and RPM range.
An HLKD 190 feeds more correction air to the mixing tube than a 160 jet. Together with the BE4, this results in a tuning that can be comparatively lean in the upper load range.
In a stock 10-PS engine, this is part of the original tuning. However, with a cylinder kit, machined ports, increased displacement, or a more powerful exhaust system, fuel consumption increases significantly.
Important for tuned engines
The HLKD 190 + BE4 is significantly too lean for many tuned 200cc engines
A full-throttle mixture that is too lean increases the thermal load on the engine
The main jet alone cannot always adequately compensate for an unfavorable combination of HLKD and mix tube
Rebase the carburetor after every relevant modification to the engine
Better base jet settings for typical tuning setups
As a significantly more sensible starting point for a classically tuned Vespa 200 engine, we recommend:
Proven starting point
Main air correction jet: 160
Mixing tube: BE3
Main jet: Adjust to fit the specific engine, starting from a definitely rich setting
The 160 / BE3 combination is a significantly better and more practical starting point for classic Vespa-tuned engines than 190 / BE4.
The final main jet cannot be specified in general terms. The cylinder, exhaust, air filter, intake, ignition, compression, fuel, and individual engine modifications significantly influence the actual fuel consumption.
Version with Separate Lubrication
This version of the SI24/24E is designed for Vespa engines with separate lubrication or an oil pump.
This makes it particularly suitable for PX Lusso and comparable engines where the oil is to continue being supplied via the standard separate lubrication system.
Suitable for
The SI24/24E is designed to closely match stock specifications for Vespa 200 large-frame engines. Due to its SI design, it can generally also be used on other large-frame models if the carburetor bowl, intake cross-section, and separate lubrication system are compatible with the vehicle.
Vespa Rally 200
Vespa P200E
Vespa PX200 E
Vespa PX200 E Lusso / EFL / Arcobaleno
Vespa PX200 Elestart
The carburetor can also be used on various Vespa 80-, 125-, 150-, and 180-cm³ large-frame engines if they are converted or tuned to accommodate an SI24.
In these applications, this is not the standard carburetor setup. The intake bore, carburetor bowl, jet configuration, and, if applicable, the separate lubrication system must be compatible with the respective engine configuration.
Technical Specifications
| Manufacturer / Distributor | POLINI |
|---|
| Carburetor Base | Spaco / Dell'Orto SI |
|---|
| Carburetor Type | SI24/24E |
|---|
| Throat Diameter | Ø24 mm |
|---|
| Separate lubrication | Yes |
|---|
| Internal Polini machining | No additional flow-side machining |
|---|
| Main jet as shipped from the factory | 116 |
|---|
| Factory-installed mixing tube | BE4 |
|---|
| Factory-installed main air correction nozzle | 190 |
|---|
| Secondary nozzle, ex-factory | 50 |
|---|
| Recommended starting point for tuning | HLKD 160 / BE3 / Adjust the main jet to match the engine |
|---|
| Primary application | Vespa PX200 / P200E / Rally 200 and comparable SI large-frame engines |
|---|
| POLINI Code | 583 |
|---|
Tuning after installation
Consider stock jet settings only as a starting point for engines that are close to stock specifications
For tuned engines, it is advisable to select the HLKD and mixing tube before adjusting the main jet
Start with a sufficiently rich main jet and fine-tune it step by step to the specific setup
Check the full-throttle range under actual engine load
Take ignition timing, compression, and thermal load on the engine into account
Re-check the fuel injection settings after making changes to the cylinders, exhaust, air filter, or intake system
Conclusion
The POLINI SI24/24E is a solid, stock-based SI carburetor for the Vespa PX200 and other compatible large-frame engines with separate lubrication.
It is important to have the right expectations: Polini does not supply a tuning carburetor that has been internally modified for increased fuel flow, but rather a Spaco/Dell'Orto SI24 that is largely stock.
This serves as a good foundation for an original or mildly modified engine. For classic tuning, however, the included 190 / BE4 setting should be examined critically. It originates from the stock-close 10 PS PX200 environment and is significantly too lean for many performance-tuned engines.
With HLKD 160 and BE3, you get a much more sensible starting point. The main jet is then safely adjusted from rich to lean to match the actual engine.
FAQ on the POLINI SI24/24E
The carburetor is based on a Spaco/Dell’Orto SI24/24E. Polini does not perform any additional internal flow modifications on this model.
No. The POLINI SI24/24E is built close to stock specifications. A BGM PRO Faster Flow, on the other hand, is specifically modified at points relevant to fuel flow and is therefore better suited for performance-tuned engines with increased fuel requirements.
The carburetor is supplied with a main jet of 116, a BE4 mix tube, a primary air correction jet of 190, and a secondary jet of 50.
The combination of a 190 main air correction jet and a BE4 mix tube originates from the stock-based 10-PS PX200 setup. In a tuned engine, fuel consumption increases significantly. The 190 main air correction jet supplies a comparatively large amount of correction air, and this combination can result in a significantly lean mixture in the upper load range.
A proven starting point is the HLKD 160 in combination with the BE3 mix tube. The appropriate main jet depends on the specific engine and should be determined based on a sufficiently rich mixture.
Yes. This SI24/24E version is designed for engines with separate lubrication or an oil pump.
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