You're 100% correct BUT a little black smoke on a high power demand shows the engine is actually working at the power you need. Sounds to me like that cat needs more fuel.
RSI it's not hard at all depending on the engine. My 1025r it took literally 5 minutes for me to give it another 5hp. About an 1/8th turn on the fuel screw and I don't get black smoke unless the engine is really working hard then I can see a faint smoke trail, that is exactly what you are looking for. The 1025 is turned WAY down for emissions. The same engine is used on the 32hp models.