Are you running itr with the stock muffler? you'll get more RPMS with an open muffler, the other thing is you can open the venturi by scraping the aluminum with an exacto or if you arecarefull enough to do it with a dremmel just make sure you don't damage the bronze fitting that's coming out on the venturi, you want to enlarge the venturi to about 3/8" diameter, Also is your carb twin needle or single needle? single needle carbs don't work well for R/C applications, the other thing you'll need to do ist take the back cover plate and lift the reed valve stop plate just to where a 1/8" drill or allen wrench can pass in between the stop plate and the reed valve, with all these changes you should be able to spin a 18X6W APC prop (top choice for the Ryobi) at about 7600- 7800 RPM considering that you are several feet above sea level, I am spining mine at 8300 but I am at sea level