This is the standard 2.0kg/35mm Dellorto carburetor slide spring for VHB carbs as used on big twin Guzzis from the late 1960s until the mid-1980s. Nuovo Falcone, Ambassador, Eldorado, V750 Special 1969-1971, 850GT, V7 Sport, 750S, S3, 850T, T3, T4, Convert, G5, CX100, 1000SP.
Outside of the United States after 1980, VHB carbs were still the stock carburetors, and this was the original spring used on SP II, California II and 850T5.
Also fitting Benelli 900 SEI. Also some Ducati and Morini models. Dellorto number 7448-61, Guzzi part number 13937100