Vespa Dellorto SI 20/20 "D" Carburetor Pre-Mix (DW-23917700)

The Dellorto Si is the range of carbs that has been fitted to the rotary valve engines of Vespa.

The big advantage of the Si carbs is the very short induction way and the completely simple setting up process. They differ very much from the usual carbs and miss the usual needles and atomizers.

The very short induction way gives a very responsive engine. They are a good choice even for fast road going with rotary valve induction. So we had 15 bhp readings on our P4 dyno at the rear wheel with the Si 24 carbs.

There is one disadvantage: On thermal high stressed engines (eg Polini cast iron cylinder kits with racing exhausts) the short induction way gives a critical cooling effect.