What carburetor is best for a Vespa?

OK, you changed the exhaust on your stock Vespa and are thinking of a better carb. What are your options?

There are three basic types. From worst to best: old-tech original style, roundsldes, and flatslides/D-slides:

Old-school

Dell'Orto or Jetex/Spaco 17/22/24mm copies of the original design from 300 years ago. Fairly cheap. The benefit of some of them of course is that the fuel is premixed, though most aren't. One option is to upgrade to a 24mm.

Roundslides

Mikuni and Keihin (Japan), or Dell'Orto (Italy) up to 28mm. Roundslides are a step up in technology from the original-style carbs, giving better throttle response and tuning capability (i.e., more things to tinker with if you want it just perfect). OK option, but more expensive. Japanese carbs have the best reputation but, depending on your location, people might have more experience with Dell'Orto, especially in the UK, though dirtbike shops anywhere are a good source for parts and tuning of Japanese carbs. Nonetheless, people don't seem to use these much on Vespas.

Flatslides and D-slides

Again, all three companies offer carbs ranging from 24 to 32mm and up. Flatslides give better throttle response than roundslides because of the design of the slide, as well as incorporating other new design features. D-slides improve upon flatslides, reducing air turbulence in the carb, and are the best. Keihin PWK D-slides are great carbs, better than overpriced, inferior Dell'Orto VHSA/B, and, some say, easier to tune than Mikuni, though others like the TMX system. (Read the Scootering showdown for the lowdown on PWK vs. Dell'Orto.)

These carbs are quite expensive, or we at scootRS have pattern PWK cheap. We'd recommend the 24mm PWK-type flatslide on most setups with a tuned exhaust, unless a highly tuned kit, in which case the 28/30mm. It's a very good setup.

Some feedback on our PWK:

  • I run the 24mm scootRS [Keihin PWK] copy and am very pleased with it. The pick up on them is instant and it was very easy to set up. Would certainly recomend them to anyone.
  • For all you carb heads out there I've just fitted an oval bore 28/30mm D-slide carb [from scootRS] onto my 210 and it knocks the socks off any Dellorto. Cheap Asian goods aren't what they used to be. Go on, save some money and invest in some good cheap performance.
  • While in Australia this year I saw a back to back dyno test comparing Milkuni and Keihin 35mm carbs on a 250cc two stroke cart engine. The difference was 2hp, not a lot but enough to knock half a second off a lap. The most amazing thing was the way you could slow down the cart into a corner using engine braking and then floor the throttle with out the usual Amal/Dellorto gurgling. This is purely down to better air flow through the venturi.

Extras

You need a new manifold with all of the above carbs, so factor each manifold's cost into the price. (We include manifolds in our carb kits; not sure who sells Dell'Orto ones, or what all mixes and matches.)

You also need a our foam filter.

Have fun!