Two cycle engines are designed to run at a high RPM. If they are over prop'ed they will seem to run good and you'll fly for years that way. If you tune your prop for RPM's you'll be amazed how much more performance you'll get. I tune my engines for a 12,000 to 14,000 RPM's. Props are cheep. Buy several and test them. Large diameter / low pitch = more pulling power with lower speed (like first gear in a car). Small diameter / high pitch = less pulling power with higher speeds (like fifth gear). Depends on your plane and flying style.

Skyhawk