SI Carburetors are original parts for all PX Vespas. When ordering, please make sure to note which version you’ll need, with or without an oil pump. The 24er carburetor is the first tuning step for all PX80-150’s. You can mount both 20er SI and 24er SI carburetors on old Vespas with slide valve induction, just make sure you order the right PX Air filter. Induction jets will have to be adjusted.