I am toying around with several Ryobi 31CC motors. Through all the great info here, I was able to convert them and actually flew one on my Great Planes Giant Supersportster. The plane handled very well but the power was lacking. With a 18X8 prop, I was only turning around 6300 RPMs. My goal was to turn at least 7000 RPMs.
After reading all the threads in the Conversion Forum concerning Ryobi's. I ordered several Frank Bowman rings, By the way, Frank is a first class person. He was very patient with me and answered all my questions about the rings and their installation. Next I got several of the 11.1 mm walbros with the high & low needles and primer. The engine on my test stand turned a 16x8 prop at 7800 RPMs with both mods. A gain of almost 800 RPMs. Here is what I am up against. With all new gaskets and the carb tuned for max RPMs and good throttle response. I can't get the idle below 3000 RPMs and the engine slowly dies if left at and idle. I have checked for air leaks and all looks good. The engine transition to full RPMs instantly. Is this a common problem when going to a bigger carb or am I not doing something right. I adj the high speed for max RPMs and the go 1 click rich. Then I hold the idle up a little and adj the low speed for the best idle and transition.
The motor with Frank's ring that is on the plane will idle at 2200 but it has the stock 7.9 mm carb and will only swing a 18x8 prop 6700. I did gain about 400 RPMs with just the ring change only. I am going to try a APC 18x6W and want to use the 11.1 mm carb if I can. The 11.1 carbs I have are WT-600 and WT-610. I also have 2 others that have 34 in the venturi. The 11.1's have 28. I am also running the stock mag ign with a lightened flywheel. I would like to use the motor on the test stand with the larger carb as it seems a lot stronger but the idle issue prevents it. I have not run this motor with an 18 inch prop yet. Will a larger prop allow the motor to idle lower? Any help will be greatly appreciated. Sorry for the long post but I wanted to include as much info as I could as to what I have done so far. Thanks again. Pat