Saito's will be rich on the low end from the factory. Leave it that way for a while. A lot of your flying is done on the low speed needle (1/2 throttle or less), so having this rich helps. Also, at idle, there isn't much air flowing over the head to cool the engine, so more oil and fuel helps keep it cool. Idling is the roughest time on any air cooled engine.
It also sounds like you might be a bit lean on the top end. That usually causes variations in the rpm's at WOT. Try opening it up, to about 300 RPM's below peak. If it still runs erratically, then you may have an airleak somewhere.
After you have a gallon through it, then start leaning up the low end to get it like you want it.