I'm assuming this is a mixture problem, because I've only noticed it since moving to GA and only when it's hot/humid as hell out, but... Something about that seems too easy.
The bike: 76 ET3 with 135 kit but otherwise stock
The symptoms: seems to be ok at speed, and *usually* idles fine. But in low throttle ranges (takeoff or gradual decel) it will suddenly and severely splutter, sputter, and occasionally vocally misfire (not a "bang" but a big "puff").
Since it doesn't do this at all Fall/Winter/Spring I'm inclined to say something is off with my mixture at the low throttle range with regard to hot dense air. However, what's fishy is 1) it only does this maybe 1/3 of the time (e.g. takeoffs), and cranking the throttle certainly helps but it isn't a magic bullet - sometimes it just keeps it alive while spluttering at higher RPMs for a bit (10s?) before it ACTUALLY clears up.
These caveats have me worried it could be some weird electrical gremlin (CDI going out, etc)