Hmm, interesting. I had just adjusted the valves before I noticed the hiccup but very confident they are set to perfect .022" and .024". Granted, they were set cold. Weak springs is a new one to me (hell, most of my toys don't even have cams and valves!!) but logical enough. I have seen a torque wrench type tool that can check spring pressure while the spring is still installed. I'll see if anybody I know has one. Otherwise... leak down wouldn't hurt. I am actually resisting the temptation to pull the head, just for a look see. I don't know if it is the totally flat head or the one with a little bit of bowl to it. Likely stock. (whichever was stock on a 1996 supersprint)
Having just had the carbs off for a through once over it is plausible a chuck of crap got in the idle circuit. Usually quite scrupulous but those are some tiny little passages.