Hi
I have an .28RR and I also find it a little difficult to tune it just right. Last weekend I noticed a leak on my carburator, exactly where the plastic and metal comes together. Then shortly after my engine died, probably because of the leak, which I believe have caused the engine to run lean at high revs (the piston got stock and when I took it apart it had a nice little scratch in the piston and cylinder). The bearings also felt pretty loose, so they were gone also. So I guess that the carbs on the Axial engines are junk.
Another thing I have noticed regarding my .28RR is how high it has to be in temps to run at it's best. My .28RR had to be around 165 C (330 degrees fahrenheit) to run good! Any lower and it struggled to take the revs. I guess running at these high temps also wears out the bearings and piston/cylinder faster.

Cheers
Tommy