AV8TOR,
I have a GX 31 on a 1/4 scale Fleet biplane that weighs 20 #. C-H ignition. It flies it OK but no power house... all acrobatics will lose altitude. I have 18-6(7600 RPM), 18-8(6800),18-10(6200), and 20-6(5600). All will fly it but the 18-8 is best all around. The 18-6 climbs best. I don't keep flight logs but guess it to have flown over 100 hours. The most dependable engine I ever had. It has never quit me. Stock carb. Mine starts like this.....choke flip it switch off 4 times, switch on, fires up most times on the first flip. Then let it warm up 2 or 3 minutes and it will take throttle. Be careful about nose over. I bent my crankshaft but managed to straighten it. It was a "Classic" nylon something or other. I use all wood props now hoping if I nose it over again it will break the prop instead.

Jerry