1976-85 Derbi moped engines (for sale in the USA) came in three speed versions:
30mph (2.0hp) 12mm xxx no restrictor, 1 – 1mm variator limiting washer (gas mileage 117 mpg)
25mph (1.5hp) 10mm intake restrictor, 1 – 4mm variator limiting washer (gas mileage 130 mpg)
20mph (1.0hp) 10mm intake restrictor, 2 – 4mm variator limiting washers
1985-89 Derbi moped engines (for sale in the USA) came in one speed version:
30mph (2.0hp) 10mm intake restrictor, 1 mm variator limiting washer
43mph actual when de-restricted!