I presume that this is an ABC type construction engine. In which case, the piston will be tight until you've ran about a dozen tanks of fuel through it (at least!). After than, it should free up a bit and idle better. Make sure you run it really rich while you are breaking it in so as not to damage the engine. Do this for a dozen tanks of fuel and you should notice the improvement.
In the mean time, I'd set the idle a bit higher so it shouldn't cut out as easily, but still leave some movement on the trim (or if you've got a throttle cut switch, use that) so that you can still stop the engine when you land.