Grump, I've noticed those subtle changes as well in sound, how it starts (today it is 83 and about 1 billion percent humidity, and it started like a pain in the butt, until it warmed up for about a minute of consecutive running, but keeping it running till that time was a bit annoying, wanted to die with full and no and partial choke, but once warmed up, ran like a beastie, nice, smooth, powerful. I did close my sparkplug gap from 0.9 to 0.8mm yesterday just to see how it would run, that shouldn't have that much effect, but....
