I have a saito .56 and it sets idleing for long periods of time and comes right back up . All my saitos have been able to hold a good low idle ( under 2K ) for an extended period.

Check you valves and see if they are set right, that will make a difference in how it runs also. What prop are you running on it? That could make a difference too.

How is your engine mounted ? If inverted , that can cause problems.