▁hurried ly ▁re - des igned ▁for ▁the ▁ 1 9 7 6 ▁season ▁with ▁a ▁more ▁rounded ▁fuel ▁tank . ▁▁ ▁In ▁ 1 9 7 5 ▁Duc ati ▁offered ▁hand - built ▁production ▁rac ers , ▁the ▁' square ▁case ' ▁ 7 5 0 SS ▁and ▁later ▁ 9 0 0 SS ▁models , ▁built ▁in ▁limited ▁numbers . ▁ ▁Sales ▁of ▁the ▁ 9 0 0 SS ▁proved ▁so ▁strong , ▁and ▁sales ▁of ▁the ▁ 8 6 0 GT / G TE / G TS ▁so ▁weak , ▁that ▁production ▁of ▁the ▁ 9 0 0 SS ▁was ▁r amp ed ▁up , ▁and ▁it ▁became ▁Duc ati ' s ▁# 1 ▁s elling ▁model . ▁▁ 1 9 8 0 s ▁ ▁Duc ati ' s ▁liquid - co o led , ▁multi - val ve ▁V - tw ins , ▁made ▁from ▁ 1 9 8 5 ▁on , ▁are ▁known ▁as ▁Des mo qu attro ▁(" des mod rom ic ▁val ve ▁four "). ▁These ▁include ▁the ▁ 8 5 1 , ▁ 9 1 6 ▁and ▁ 9 9 6 , ▁ 9 9 9 ▁and ▁a ▁few ▁prede cess ors ▁and ▁derivatives . ▁ ▁The ▁Duc ati ▁Pas o ▁was ▁introduced ▁in ▁ 1 9 8 6 ▁with ▁the ▁Pas o ▁ 7 5 0 , ▁followed ▁in ▁ 1 9 8 9 ▁with ▁the ▁Pas o ▁ 9 0 6 . ▁The ▁final ▁version ▁came ▁in ▁ 1 9 9 1 ▁with