First off I would like to point out that Satio recomends against using fourstroke fuel in their engines due to the lower oil content. They instead recommend using two stroke glowfuel of at least 18% oil. I have owned a Satio 91 for quite some time now and it is a great engine. I usually run either Powermaster 20/20 or Morgan's 30% Heli fuel in mine with excellent results and power. You usually richen the engine off peak about 200 to 300 rpm for flying. I usually tach around 10000 rpm rich with a 14x6 but I prefer the Apc 15x6 prop instead. With 30% fuel I can run this prop about 9200 rpm with excellent results.

I too believe the high speed needle is your problem. There should not be any play in the needle valve. Check the O ring and you might have to use the previously mention idea about using fuel tubing to help seal the needle valve. Good luck with the engine.