I have a OS Surpass ii with pump and the engine runs well , good power and transitions well. I am using a 16x8 prop. I have set the high speed 300 rpm less than peak. Then I set the low speed needle. The problem is I can not get the engine to idle low enough so the plane isn't at a fast taxi. I can get it to about 2250 RPM and will idle there reliably for about 30 seconds maximum and is running rough. then quits. If I lean the idle mixture more it wont idle. If I richen up the idle mixture it will not idle as low. I have little experience with 4 strokes so any comments would be helpful.

I see other 4 strokes idle low enough what am I doing wrong?? What is the lowest reliable RPM I can expect at idle with this engine?