The stock CNS V3 carb and exhaust has provided me with reasonable smoke free speed, quiet and fuel economy over the summer. I do mods anyway; it could always be better. A nagging hard to find problem in performance and fuel economy like you described was traced back to the air filter. This stock filter may have to be absolutely dry and oil free to flow air properly. Every mile you ride may result in lower performance and fuel economy as the filter takes on 2 cycle oil. If you don't believe it could be that serious; just ride with the air filter removed, Rupp Black Widow style and note the difference. I do not know if the filter can be cleaned. There is nothing said in the Skyhawk manual about air filter maintenance. If there is a better made to fit filter replacement, I am not aware of it.