POLINI SI26/26E – Production-style SI carburetor with a nominal diameter of 26 mm for the Vespa PX200
Version with separate lubrication – solid stock base, but without internal flow optimization
The POLINI SI26/26E is a classic SI carburetor for Vespa large-frame engines with separate lubrication. Despite the designation SI26/26E, the actual bore diameter is only about Ø24.8 mm due to the design. The slightly smaller actual bore diameter is necessary to ensure that the throttle valve still has a sufficiently wide and stable guide within the carburetor body. Polini sources the carburetor from Spaco/Dell’Orto; technically, it is a near-stock version without any additional internal machining of the fuel or air passages.
This makes the carburetor an excellent replacement for a worn or damaged stock SI26/26E and a solid starting point for classic PX200 setups.
However, it is important to understand the distinction: The POLINI SI26/26E is not comparable to a BGM PRO SI26 or SI26 Faster Flow that has been extensively modified in-house. With the BGM PRO SI26 Faster Flow, the areas relevant to fuel delivery are specifically modified to ensure a higher fuel flow rate in high-performance engines. The POLINI carburetor, on the other hand, essentially adheres to the stock SI design.
SI26/26E
approx. Ø24.8 mm
Separate lubrication
Spaco / Dell'Orto base
PX200
Stock jet settings are usually too lean for tuning
The POLINI SI26/26E at a Glance
Approx. Ø24.8 mm: classic SI26/26E size for Vespa 200 Largeframe
With separate lubrication: for engines with a stock oil pump
Spaco/Dell'Orto base: stock-like carburetor without additional Polini flow modifications
Fuel delivery close to stock: a solid foundation for stock and mildly modified engines
Well-tuned right out of the factory: HD 120, ND 55/160, BE3, and HLKD 160
Good starting point: The HLKD 160 and BE3 are a much better fit for classic tuning setups than the lean 190/BE4 combination found on many stock PX200s
Fine-tuning required: Select the main and secondary jets to match the specific engine
SI26/26E – nominal 26 mm, actual approx. Ø24.8 mm
With this carburetor, the designation 26/26 does not mean that the passage has actually been fully bored out to 26 mm. The actual passage diameter is approximately Ø24.8 mm.
The reason for this is design-related: If the cross-section were enlarged further, there would be insufficient material remaining in the area of the throttle valve to ensure a sufficiently stable guide. The approximately 24.8 mm therefore represents a sensible compromise between a larger passage and a secure guide for the throttle valve.
Nominal Dimension and Actual Bore
Designation: SI26/26E
Nominal size: 26 mm
Actual bore: approx. Ø24.8 mm
Reason: sufficient guidance and stability of the throttle plate in the carburetor housing
Production-spec SI—not an internally optimized Faster-Flow carburetor
Externally, various SI26 and SI26 carburetors look very similar. However, what matters is what happens inside.
The POLINI SI26/26E is a stock-based Spaco/Dell’Orto carburetor. Polini does not modify the internal fuel and air passages in the same way as is done with a carburetor specifically prepared 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 SI26/26E vs. BGM PRO SI26 Faster Flow
| Feature | POLINI SI26/26E | BGM PRO SI26 Faster Flow |
|---|
| 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 tuned to the specific engine setup |
Factory-set with a sensible 160 / BE3 base jet setting
The POLINI SI26/26E comes with a significantly more sensible base tuning than many stock PX200 carburetors:
Main jet: 120
Secondary jet: 55/160
Mixing tube: BE3
Main air correction jet: 160
The combination of HLKD 160 and BE3 is particularly effective. This setup provides a much more practical starting point for classic Vespa-tuned engines than the very lean combination of HLKD 190 and BE4, as used in certain stock PX200 models.
Nevertheless, this jet setup should also be understood only as a starting point. The appropriate main and secondary jets always depend on the specific engine. The cylinder, exhaust, air filter, intake system, ignition timing, compression ratio, and individual engine modifications all influence the actual fuel requirement.
A Good Starting Point for Classic Tuning
HLKD 160: a proven size for many tuned SI engines
BE3: classic mixing tube for many PX tuning setups
HD 120: a usable starting point, but not a one-size-fits-all solution
ND 55/160: also needs to be adjusted based on actual engine performance
Basic rule: it’s better to start on the rich side and then fine-tune precisely
Version with separate lubrication
This version of the SI26/26E is designed for Vespa engines with separate lubrication or an oil pump.
This makes it particularly suitable for PX Lusso and comparable engines where oil is to continue being supplied via the standard separate lubrication system.
Suitable for
The SI26/26E is designed to closely match stock specifications for Vespa 200 large-frame engines. Thanks to its SI design, it can generally also be used on other large-frame models, provided 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 SI26.
In these applications, the carburetor setup is not the standard configuration. The intake cross-section, carburetor bowl, jet configuration, and, if applicable, the separate lubrication system must be compatible with the respective engine configuration.
Technical Data
| Manufacturer / Distributor | POLINI |
|---|
| Carburetor Base | Spaco / Dell'Orto SI |
|---|
| Carburetor Type | SI26/26E |
|---|
| Nominal Size | 26 mm |
|---|
| Actual bore | approx. Ø24.8 mm |
|---|
| Separate lubrication | Yes |
|---|
| Internal Polini machining | No additional flow-side modification |
|---|
| Main jet, factory setting | 120 |
|---|
| Factory-installed mixing tube | BE3 |
|---|
| Factory-installed main air correction nozzle | 160 |
|---|
| Secondary nozzle, factory-installed | 55/160 |
|---|
| Basic Nozzle Configuration | HLKD 160 / BE3 / HD 120 / ND 55/160 – as a starting point, to be customized |
|---|
| Primary application | Vespa PX200 / P200E / Rally 200 and comparable SI large-frame engines |
|---|
| POLINI Code | 617 |
|---|
Tuning after installation
Consider the included jet settings a good starting point, not a universally applicable final tune
HLKD 160 and BE3 can be retained in many classic tuning setups
Start with a sufficiently rich main jet and gradually fine-tune it to the specific setup
Check the full-throttle range under actual engine load
Take the engine’s ignition timing, compression ratio, and thermal load into account
Re-check the fuel mixture after making changes to the cylinders, exhaust, air filter, or intake system
Conclusion
The POLINI SI26/26E is a solid, stock-close SI carburetor for the Vespa PX200 and other compatible large-frame engines with separate lubrication.
It’s important to have the right expectations: Polini does not supply a tuning carburetor internally modified for increased fuel flow here, but rather a largely stock Spaco/Dell’Orto SI26.
A positive feature is the included base jet set with HLKD 160 and BE3. This makes the POLINI SI26/26E significantly more practical right out of the box than many stock PX200 carburetors with a lean 190/BE4 combination.
However, the included HD 120 and ND 55/160 are only starting points. The final tuning must always be tailored to the specific engine and should definitely begin with a sufficiently rich setting.
FAQ on the POLINI SI26/26E
The carburetor is based on a Spaco/Dell’Orto SI26/26E. Polini does not perform any additional internal flow modifications on this model.
No. The POLINI SI26/26E is built close to stock specifications. A BGM PRO SI26 Faster Flow, on the other hand, is specifically modified at points relevant to fuel flow and is therefore better suited for tuned engines with increased fuel requirements.
The carburetor is supplied with a main jet of 120, a secondary jet of 55/160, a BE3 mix tube, and a main air correction jet of 160.
With a primary air correction jet of 160 and a BE3 mix tube, the POLINI SI26/26E already offers a significantly better starting point for classic Vespa tuning. However, the 120 main jet and 55/160 secondary jet must still be checked and adjusted to suit the specific engine.
Yes. The HLKD 160 and BE3 provide a good starting point, but the main and secondary jets depend on the specific engine. The tuning should always be checked under actual load and determined starting from a sufficiently rich setting.
Yes. This SI26/26E model is designed for engines with separate lubrication or an oil pump.
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