My friend's YS110 is having idle problems. The top end is fine but when you bring it to an idle, about 2,500 RPM, the engine will idle for like 8 secs then it will speed up and die. We tried to richen and lean up the low end to see where it leads, it still does the same. There is no fuel leaking from the carb, all looks good and its a new engine. Any ideas? Thanks!