Generally, the only engines that benefit from porting are the smaller, weedeater type engines. The porting on most chainsaw engines is more than adequate for airplane use.

It is just an aerodynamic fact that a large diameter prop turning slower is more efficient than a small prop turning faster. One exception to this rule in a small way, would be a racing plane that benefits from a smaller diameter, but higher pitch prop. Your observations are correct; somewhere around 6500 to 7500 rpms is where most people run their gas engines in most airplanes nowadays. Part of this is the popularity of 3D flying, and the necessity for as much static or low speed thrust as possible for that type of flight, which of course a large diameter, lower pitch prop provides. Another couple of factors are, as you mentioned, prop tip speed, and noise. As the prop tips get closer to the speed of sound, they lose efficiency and get noisy. The faster the prop tips are going, the more noise they are likely to create. Most people don't realize how much prop noise contributes to the overall noise a plane generates, but it can be quite significant. Lastly, if the prop load is too small, as it might be when propping for higher rpms, the two stroke engines tend to have an annoying "four stroke" burble in the mid range throttle area that can be hard to tune out with the current Walbro or Zama carbs that don't have a midrange mixture adjustment available.

So the bottom line is, really, that your porting is fine as is, and only might benefit from a slight cleaning up of any casting flaws. The original carb will work fine as well. The two significant improvements you can make to the engine are to use a free flowing muffler, and install electronic ignition. Then you've got a fine airplane engine in that Poulan. And if noise in not a consideration in your case, and you don't want to fly 3D, you can always prop it to turn 8000 or so and it will be fine.

As an added note; most full size airplane engines only run around 2700 rpms at full throttle, and maybe 2500 rpms or less for cruising flight.

AV8TOR