runner st125 gearup help

was just thinking about maby geting a gear up kit for better fuel econamy in thory if i was to fit a gear up kit to my st wudent i be able to reach the same speeds at lower rpms becuse of the fact that the gearing is taller an there by saving fuel im geting about 90 mile to a tank at the moment i wud like to be able to do a 100 or more i my thinking is incorrect plese tell me but if im right witch kit wud be the best to go for for what im after wud idealy like to not lose to mutch accelaration

sadley not for me to sound like a twat but its in how much you use your right hand.Once you go down the road of putting big carbs on and performance pipes thats when you see how much your fuel is being chucked away.try a leader jet kit tey maydo one but you cant have performance with out the cost thats why all real bike tunners dont stick carbs on from 22mm and then jump to 34mm.there are other factors that you can check like tyre pressure,spark plug