Usually the problems people seem to have with ST's comes down to tuning (particularly low end), glow plug choice, and fuel mix. For my GS40's and G61 (all ringed) I use OS5 glow plugs and only 5% nitro. Any more nitro than that's just a waste of space and will make them hard to run nicely. Tuning the idle mixture takes a few minutes while breaking in the engine and typically never needs changing again unless you have dramatic changes in fuel mix or altitude.

Matt