They advertize that these engines are broke in at the factory so a begginner can take it out and fly. HOWEVER, Use the instructions for tuning as a guide and ensure you have a reasonably rich mixture (visible smoke at wide open throttle (WOT) and a nice gooey resedue) You can normally attain this by running the engine at WOT while the plane is restrained slowly turning the needle valve in (clockwise) a click or two at a time with at least 15 second pauses between clicks so the engine can react to the change. As you do this you will notice that the engine will begin to run faster. When you reach peak RPM turn the needle valve out (counter clockwise) about 2-4 clicks. Check throttle response. Bring the engine down to idle (adjusted so the plane will not pull forward in short cut grass) let it idle for about 20 seconds. Then advance the throttle to full (Do not jam it to full but reasonably advance the throttle, this should take about 2 seconds) and see if the engine stutters stumbles or stalls.