sh aft ▁drive ▁pul le ys ▁indexed . ▁On ▁older ▁Duc ati ▁mot ors , ▁prior ▁to ▁ 1 9 8 6 , ▁drive ▁was ▁by ▁solid ▁sh aft ▁that ▁transferred ▁to ▁the ▁cam sh aft ▁through ▁be vel - cut ▁g ears . ▁This ▁method ▁of ▁val ve ▁actu ation ▁was ▁used ▁on ▁many ▁of ▁Duc ati ' s ▁older ▁single - cy l inder ▁motor cy cles ▁— ▁the ▁sh aft ▁t ube ▁is ▁visible ▁on ▁the ▁outside ▁of ▁the ▁cyl inder . ▁ ▁Duc ati ▁is ▁also ▁famous ▁for ▁using ▁the ▁des mod rom ic ▁val ve ▁system ▁champion ed ▁by ▁engineer ▁and ▁designer ▁Fab io ▁Tag l ioni , ▁though ▁the ▁firm ▁has ▁also ▁used ▁engines ▁that ▁use ▁val ve ▁spr ings ▁to ▁close ▁their ▁val ves . ▁In ▁the ▁early ▁days , ▁Duc ati ▁reserved ▁the ▁des mod rom ic ▁val ve ▁heads ▁for ▁its ▁higher ▁performance ▁b ikes ▁and ▁its ▁race ▁b ikes . ▁These ▁val ves ▁do ▁not ▁suffer ▁from ▁val ve ▁float ▁at ▁high ▁engine ▁spe eds , ▁thus ▁a ▁des mod rom ic ▁engine ▁is ▁capable ▁of ▁far ▁higher ▁revolution s ▁than ▁a ▁similarly ▁configured ▁engine ▁with ▁traditional ▁spring - val ve ▁heads . ▁ ▁In ▁the ▁ 1 9 6 0 s ▁and ▁ 1 9 7 0 s , ▁Duc ati ▁produced ▁a ▁wide ▁range ▁of ▁small ▁two - stroke ▁b ikes , ▁mainly ▁sub - 1 0 0   cc ▁capac ities . ▁Lar ge ▁quantities ▁of ▁some ▁models ▁were ▁export