I was running the STS piston sleeve, crankshaft, bearings in a NovaMax crankcase with a Nova Carb. Surprisingly, the "problem" associated with this engine is gone. The normal low end "rich" spluttering was no longer evident. I have only changed the carb and was using a kyosho 6mm pipe (instead of 7mm). This engine seems to be as fast as the Novarossi engines. My lsn needle was 2.5 turns and HSN was 4.5 turns which is pretty similar to my NSR settings.
I would also suggest that the crankshaft be polished if you intend to use the original STS crankcase.