Yes indeed I appreciate there are many factors.
I only wanted to address the dry air /moist air factor irrespective of the local oxygen content variations.
I hope I did that.
Cheers.

Thank god all mine carry 12v DC then, eh?

If I could understand a word of it, you very likely did

Apparently I was wrong to assume it was the oxygen content in moist air that was the contributing factor to improved fuel economy. It would appear that it is the density of the air that makes the difference, moist air being less dense than dry air

I guess so. It was just the mention of two strokes reminded me of my Yamaha FS1E back in the day, that regularly used to die in the rain. Then there was the time I tried to push the HT lead properly onto the spark plug whilst riding along. I must have got about 6000 volts through me.