IMO there are two characteristics of Super Tigres that can cause symptoms such as yours. The first is that they seem to take a long time to break in, perhaps due to the nature of the rings versus the material of the cylinders. At any rate, with my two ST motors this was an issue that caused stalling. My ST60 probably had 30 flights on it before I could consistenly rely on it. The only solution until then seemed to be to run it quite rich and with a fairly high idle speed...and to not let it idle for any length of time before takeoff.
The second issue is carburetion. If you look on the ST site for parts data you will note that the carb and its components (including the needle assembly) are identical for the 60 and the 90, and if I recall (not looking at the site right now), one of the smaller model motors (45?) as well. While this might have saved some money it represents, again IMO, an extreme and unhappy compromise. My 90 never ran as well as the 60, and one of the most experienced flyers in our club told me the smaller motor runs best of the three. It appears the engineers tried to design a carb that would suit all three sizes, but I fail to see how a single venturi and needle size could be anywhere near optimal for three motors with significantly different displacements.
The good news is, if all of this is accurate, that the 60, once broken in, is a reliable and quite powerful motor and mine has been flawless after it got over its initial teething pains.