The SI carburettors are fitted as standard to all Vespa Largeframe models (apart from the GS160/SS180). Their design is simple in terms of its structure and thanks to the main jet, main air correction jet, idle jet and choke jet, throttle slide and idle running mix regulating screw, they offer similarly precise setting options as the larger drum or flat side carburettors.
They are also easy for non-professionals to tune as adjusting the main jet normally achieves the required effect.
Their shorter intake duct helps the throttle response of the engine and makes the SI carburettors the first choice for disc valve engines.
"Some years ago Dell'Orto made an agreement with Spaco and Piaggio to produce carbs type SI in India. So Spaco produces on license and delivers to Dell'Orto, Dell'Orto guarantees the quality and delivers the SI carbs to Piaggio for first equipment and to all other customers for after market.
