Jim, , haven't flown the Spit yet. Been windy here and as you may know we had a tornado or two pass by close last night. It hit a local airport and did some damage. I watched the storm pass and kept an eye on the local news plus saw the footage again today on several national stations, CNN, NBC, etc. Our channel-9 heli guy , Mason Dunn is an extremely good pilot and was able to capture some killer footage closeup. He runs a HD camera which is mounted underneath the copter on a turret. He really zoomed in on a Sukhoi parked near the damaged hangers.
Anyway,,, last tach I did was 8600rpm with a 17x6 APC after I wacked about 1/2" from the muffler and started running Amsoil Saber at the required 50:1 mix using premium unleaded. Will idle nice and slow all day. (Or until you run the tank dry.) Did that this evening before dinner. Also went with the NJK R7 type plug.
The engine runs nice and cool under the cowling. But then again I've hacked the crapola outta the cowl to fit it in. The velocity stack sticks thru the hole once occupied by an OS-91FX and then a ST-G-2300 cylinder head. And I cut away the muffler area as well. Leaving the muffler covered completely inside the cowl can trap alot of heat on these gassers.