Vespa Si

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  • 49.9cc displacement
  • 50:1 fuel ratio
  • 12.10 Dellorto SHA carburetor
  • 16" x 2.5" front (Pirelli)
  • 16" x 2.5" rear (Pirelli)
  • Dual variated with internal rear wheel transmission
  • 6v electrical system
  • V Belt drive



A Vespa Si
The Vespa Si (meaning yes) is the sportiest model Piaggio sold in the United States. The cantilever suspension and bulky oil filled forks make the ride very durable, stable, and comfortable, resulting in this moped being a great candidate for speed.


The Si is lighter and more compact than the Vespa Grande. It has silver 4 spoke aluminum mags that are tougher than the wire spoke wheels found on most other mopeds. It also comes stock with a variator, giving a better acceleration than it's single speed brother, the Vespa Ciao. The Si's engine is no different than any other Vespa moped engine but has a specfic looking cylinder head not found on other Vespa. It came with a Dellorto 12.10 carburetor which has a two piece lever choke, unique to Si. Hand brake and decompression levers are plastic and made by Domino. Handlebars are not adjustable back and forth, only up and down.


The Si comes with parts that are not common to any other Vespa. The 4 spoke mags are very desirable and are can also be found on other versions of Vespa mopeds only in Europe (Ciao-Mix, Bravo-Mix, etc). Also, the taillight and headlight are specific to the Si, meaning replacements will probably have to be sourced from Italy, or parts mopeds. The CEV brake/taillight utilizes a two piece bulb set up unlike other Vespa. There is also a shroud underneath the gas tank which covers a wiring harness, VIN plate, and houses the horn assembly. Si came in 20, 25, and 30 MPH versions, easily determined by the black and white sticker found on the left side of the sub frame with the side cover off stating 20, 25, or 30. Other parts for each version had MPH identifications in the respective part numbers. Example parts that made the difference in MPH were the carburetor/jet, exhaust pipe, and transmission gears. As Vespa Grande, the Si seat does also flip open where a storage compartment can be found unlike on Grande. The actual metal seat frame also has provisions for a tire air pump and is a very rare accessory. If you are lucky enough to obtain one, inside the right side cover, contained a tool kit like other Vespa. Not many tool kits seem to exsis, although kits do not differ much from other Vespa tool kits, finding a Si with one is not very common. Another not so common part to still find is the oil cup that's fastened to the gas cap. The exhaust look and design are also Si specific. It has a completely different sub frame mounting hole location, which means the exhaust will not direclty bolt up to other Vespa unless a new hole is drilled to bolt the rear exhaust flange to. The Si is also the only Vespa to be imported to the states with no factory turn signals, both front and rear luggage racks were optional though. It also was the last Vespa moped imported to the USA.


The most common Si colors for the US where black unless you're betting $20 on the original US colors with Sal Smog because then it's "charcoal black" , orange, and green. Paint codes are almost non existent and people have tried to get them from Vespa overseas but have had no luck. Rumor has it Vespa did not keep good record of Moped paint codes unfortunately. Color matching is about the only option for paint matches and restorations.

Cantilever suspension

Not found on other Vespa, this single shock absorber design made for a nice clean look since it was hidden inside the sub frame and a comfortable ride.


VIN numbers

VIN numbers can be found on a few different places. One is on the VIN plate mounted under the horn cover on the front of the frame. Subsequent places include a sticker under the seat, fastened to the seat frame. Likewise, a sticker could be fastened to the top of the frame, commonly known as the bottom of the drop tank. This was the mostly clearly visable location for obvious reasons.

Performance Parts

A large number of performance parts exist for Vespa Si. Orginially found mostly overseas, but now readily available in the States, there are numerous performance pipes, carburetors (really only one a 13.13 SHA), cylinders, engine cases, variators, CDIs, exhausts, and crank shafts available to make these pretty quick bikes. There are also "free" mods that may be done for a few extra MPH.

Si Monte Carlo

The Si Monte Carlo was the UK version. It was configured differently and those differences included: the seat and under seat storage compartment, brake/tail lamp assembly, headlamp assembly, dual rear shock absorbers, mag or spoke wheels, turn signals, and a host of different colors then US Si mopeds.

Service manual

Dellorto carb parts PDF