One of my engines is an RB X12 just rebuilt and moded. What i can tell you is that the difficult part was the first time, and this second time, the Break-In. This engines are very tight and tend to grip pistons the first tank or so, so one has to be very carefull during this period. Apart from that, it is no less or more difficult to tune than any engine. All Nova based engines use the same carburator. Never had temperature problems, and here in PERU we have kind of a tropical weather (very humid).
I also have Picco, Lauro Collari Picco, Sirio "Evo2" and Novamega engines and all of them properly tuned are good engines, each with it's own personality and power band.
My favorites in order:
1.- Sirio "Evo2"
2.- RB X12 modified by me
3.- Collari Picco
4.- Novamega (old rear exhaust)
5.- Picco XS12
It is very difficult not to mess around with carb settings, because you have to adjust engine when track, weather conditions, pipe, plugs nad gearing changes.
Of course that is all true if you are into serious racing.
Don't be afraid, just get any of the latest generation of top brand engines and just practice settings and you'll get to dominate them beasts.
Hope this helps