Identify which Piaggio/Vespa engine you have. There are three different types: Pre-2000 Piaggio engine--No catalytic converter and Dellorto or Weber 12mm carb; 2000 through 2005 Piaggio/Vespa engine--Catalytic converter and 17.5mm Dellorto carb; 2005 onwards Piaggio/Vespa engine--Catalytic converter, 17.5mm carb and slightly lower exhaust port. De-restricting for pre and post-2000 engines is done in two parts. For the post-2000 engines, there is an additional step of adjusting carburettor jetting as well.
Prepare a clean work area and make sure all necessary tools and parts are nearby and ready for use.
Open up the Vespa engine case and locate the outer engine pulley. Undo the outer pulley only. You may need an air-power impact wrench or a variator locking tool to successfully stop the pulley from spinning while loosening. Locate the cylinder washer between the inner and outer transmission pulley when exposed. Remove the washer and reinstall the outer pulley. Nothing else needs to be removed. Secure the outer pulley and close up the engine case, making sure to secure all engine case nuts as needed to factory tightness. Use a torque wrench to be sure.
De-restrict the exhaust. The second restriction on a pre-2000 engine is a small pipe coming off the exhaust which interrupts the gas flow slightly. Remove the exhaust for the work to be done. Cut that small pipe off and weld up the holes created. This is a minor restrictor and will not solve all your problems if you don't remove the pulley washer described above. Reinstall the exhaust when completely finished.
Make jetting changes. Post year 2000 engines require carburettor jetting changes. No jetting change is required for pre year-2000 engines. Find the carburettor on your scooter. All post-cat Vespa models now come with a 17.5mm carburettor. The stock main jet is either a size 53 or a 56 (pre or post year 2005 model respectively). Take the old main jet our and replace it with a larger size main jet, two to three sizes bigger (56 or a 58).
Dus een ring in de vario, een kleine uitlaatrestrictor en een paar maten kleinere sproeier.
Er staat wel niets over 25 en 45 km/h in die tekst.