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 & 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 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.
MANIFOLDS
Keep in mind that you may need a new manifold.
