I'd clean the shit out of the carbs as well and throw a rebuild kit in. My little girls lt80 was doing a similar thing last week....start up idle for a few seconds and die. I stripped the carbs and boiled the hell out them for 30 minutes in water, let dry, cleaned with brake cleaner, blew out with air, installed new carbs kit....problem solved. Idles like a champ now. Although this may not fix the run away problem...its a good start. Check for an air leak too as mentioned already.