Hey converts! just to let you know for performance I use an APC 18x6W prop and my tach readings are 8100 rpm with excellent pull on my 80" 14 lbs ryan's rebel, This is at sea level, with a fully gutted muffler, a 1/4 " aluminum spacer plate for the carb and the venturi opend at .400", I use medium unleaded gas mixed with Mobil's MX2T oil at a 50:1 ratio all of the engines that I've converted myself give this kind of reading,
I was using a 16x8 APC pattern prop and was getting around 8700 rpm's but limited on performance when I ordered the 18x6 prop through hobby people they got me the 18x6W which is designed for 3D performance, try this prop you will like the big difference in your engine's performance