i have an 81 pepi with a minarelli engine, and my sprocket sucks. its flimsy and plastic and makes my chain fall off all the time, i want to get a new one. i also want the new one to be bigger so i can get more top end. ive searched on several sites, mopedjunkyard, 1977 mopeds and others, and i was unable to find one that i knew would fit for sure. plz help.