Even with factory settings, it is very possible to run lean due to an air leak. The air leak could be a crack in the fuel tank, a pinhole leak in the fuel line (Including the pressure line coming from the exhaust ), a leaking fuel filter, Leaking carb seals (At the carb neck or around the needles), or a leaking backplate. Check the fuel line and filter first...they are the cheapest to replace.

Was the engine smoking from being hot? What was the temp? Did you see a smoke trail when running?

You can check the gears easily by looking at the clutchbell and the spur gear. Are either of them chewed? Are there missing teeth? If not, look more into your engine issue.