I have a 78 puch maxi and it only runs well with the air box off, ive cleaned the carb dozens of times and decarbonized everything. i run 50:1 ratio. what could i adjust to make it work right with the airbox on? i have a biturbo on there too if that would change anything. also is it ok to run synthetic oil in my moped? i use castor927 in my dirtbike(its fully sythentic motocross racing oil) and it works great. these questions sound kind of ameteurish but ive never heard a answer. any help is greatly appreciated!