Talking about flutter again, I also had flutter and got worse on the 3rd flight, and this is what I found.

The bellcrank in the elevator spar got loose, after tightening it got much better but still flutter at half throttle ,I'm using a Magnum 91 inverted 14/4 on wildcat YS 20/20 and OS F (it works just great),also I'm using a Hitec digital 5246 (I guess ) on 6V but even if they call for about 110+ Tq and 250+ holding power is the backlash on the gears what is causing the slop and thus flutter, so I think the answer is to get a JR servo ,anyway is cheaper than the airplane.So it is not the airplane or push rod,check the backlash(play) in the servo gears.

I'm also having problems to do the Harrier, I also have 6 flights on it all with wind of about 10-20mph, but that's the day a got to fly ,not much of a choice!.

Any suggestion on CG, etc?

The Kulbuto is a really nice maneuver to see!.

By the way on two strokes Stephan Laurens (designer) fly the Diabolic with a Super Tigre 61 in contests.