I have noticed with my Nano that the motor tends to '4 stroke' at intermediate power settings, indicating the mixture is too rich.

I was tending to avoid those settings on descent/landing just in case...

The plugs looked fine, but the exhaust was throwing a bit of black stuff onto the rudder.

I decided to have a look at the carb settings.

The jet needle was set at the 3rd slot down, whereas the Hirth manual specifies first clip position.

That made sense- I suspect the Fusioncopter guys had purposely set the mixture on the rich side while the motor was bedding in.

I reset to the first (top) slot, did a ground run then a longer flight to check operation, temps and fuel burn.

The motor runs sweet across the throttle range- EGTs and CHTs well within the green, plugs light tan.

Fuel burn over a 1 hour cruise at 5000rpm 75km/hr was 15 litres.

I'm happy with that.