ORIGINAL: RTK
Flymeaway, if you are having troubles in the air but not on the ground with run-ability then it is an air pressure problem on the carb, also as mentioned some of the carbs that came with them had very loose needles leading to problems also. If it is running hot also look at your baffling and and especially air flow, a lot of people do not pay much attention to that and any high performance engine needs a little extra in the cooling department.
I have one of the first ones made and it has not missed a beat, very smooth/linear running and gobs of power
I've been chasing this burble for five years now. New carb, tried with the velocity stack on and off, tapped and routed a pressure relief tube back to fuse, adjusted needles endlessly, new plugs, different diameter fuel lines, different oil...
The only thing I have not tried is baffling. Originally the engine was in an Extra, now it's in an MX-2. The cowls are similar so maybe baffling would help. Right now it seems that there's plenty of intake area and maybe slightly less exit area. I'll have to look into how to go about doing that since I'm completely clueless as how to do so.
Thanks.